Emergency services are continuing to help the injured after several explosions on the London Underground Tube network this morning, and on a bus in central London. BBC News correspondents are on the ground with the latest details.
Sarah Mukherjee : King's Cross : 0110 BST
The thing that strikes you is that there is virtually nobody here. This part of London normally on a Thursday evening would be very, very crowded. People would be getting the last over land train and Tube after a night out.
But King's Cross is closed and King's Cross underground is closed.
The one thing there is a queue for is the all-night newspaper stand in front of King's Cross.
People are grabbing handfuls of newspapers. One gentleman in front of me took every single paper there was and started scanning them feverishly almost as soon as he had paid as if to confirm that the horrific events were actually true.
There is very little else in the papers and, of course, very little else in people's minds.
Jeff Randall : City of London : 2230 BST
It was an early shock, but the City regained its composure pretty quickly. And once it did the stock market just about took events in its stride.
The City of London has had plenty of experience of bombings and terrorist attacks going back to the Luftwaffe in the 1940s and, of course, the IRA campaigns in the 1980s and 1990s. City folk have learnt to be resilient.
I am not saying we are not going to have a few wobbles along the way, especially if there are more bombings.
But if there are not more bombings, I do not see London's financial markets falling apart.
Margaret Gilmore : Scotland Yard : 2213 BST
There is a strong suspicion amongst security sources I have been speaking to that the bus bomb may well have been carried there by a suicide bomber.
They are investigating the possibility - only a possibility at this stage - that there were other suicide bombers amongst those who planted the bombs on the Underground.
A key question - were they foreign, or home-grown British and thus more difficult to detect?
June Kelly : King's Cross : 2115 BST
The explosion happened here between King's Cross and Holborn stations on the Piccadilly line, one of the deeper Tube lines, which made it more problematic in terms of getting to people and getting them out.
What's strange is that this area would normally be buzzing at this time but there's a very eerie calm and stillness over the whole neighbourhood.
Paul Adams : Gleneagles : 2030 BST
There was a key moment this morning in which Tony Blair found himself in the midst of a national catastrophe. He was surrounded by leaders such as George Bush who know all too well what it's like to be a leader facing a situation like this.
Mr Blair is expected to return to the Gleneagles summit this evening.
Duncan Kennedy : Royal London Hospital : 2002 BST
All sorts of injuries here associated with blasts in confined spaces. Amputations, broken limbs, airways blocked with smoke and eardrums perforated.
One doctor said he'd seen as many injuries in three hours today as he had in six months in casualty.
Jane Hill : King's Cross : 1915 BST
I've been speaking to quite a lot of hoteliers here, there are lots of small hotels in this area.
They've been inundated, the phone is ringing off the hook, because so many people are stuck in London and can't get home.
Paul Wood : New Scotland Yard : 1856 BST
Already trains are being searched so that in the morning there can be some kind of skeleton service.
They are hoping to have some kind of service in the outer part of the network tonight, but tomorrow morning there will be a skeleton service except in those areas that London Transport describe as a "crime scene" .
David Shukman : In the air over London : 1850 BST
David Shukman reports that some of London's roads are gridlocked
Traffic is moving easily over Tower Bridge, and a number of trains are starting to use the railways again, including the Docklands Light Railway.
We're beginning to see signs of life returning to normal.
But there's a different picture on the roads, with people stuck for hours, and some reports of people abandoning their cars.
Andrew Marr : Gleneagles : 1834 BST
The G8 is the biggest concentration of raw political power you get in the world, but for much of the day it has felt like a sideshow.
Blair learned about what had happened after he'd been talking to the Chinese president. He came out looking very shocked.
He got agreement that breaking off the summit would be the wrong thing to do and will try to conclude all the business of the summit. We will get the communiques on Africa and global warming tomorrow.
This was supposed to be Africa's moment, and global warming is an intensely difficult and important issue. These issues can't be pushed to one side and discussions have to be concluded. But this could be the oddest and saddest G8 there's ever been.
Luisa Baldini : Tavistock Square : 1832 BST
It is as though time has stopped here.
Apart from the casualties being moved out of the area, everything has remained as it was at ten to ten this morning when the blast happened so that forensic investigators can carry out their work.
You can still see the bus, the top deck blown off. The vertical hand-rails remain, poking into the air.
In the middle of the road you can still see cars that were abandoned, the doors still flung open.
You can imagine the panic as they tried to flee the scene.
An investigation has now begun
The office building next to the bus is splattered with blood from the explosion.
You can imagine the shock in such a busy place as Bloomsbury.
I went into one hotel where dozens of American students were huddled round a TV trying to work out what was going on.
A couple were crying, too frightened to venture out today.
Duncan Kennedy : Royal London Hospital : 1830 BST
The doctors, nurses and victims we've been speaking to simply cannot believe what has happened. The raw figures from this hospital are these: one person has been confirmed dead as a result of their injuries. More than 200 have been brought here, seven of those remain in a critical condition.
Mark Easton : King's Cross : 1820 BST
Just after 0900 I looked out of my car and saw the soot-blackened faces of men and women who might have been trapped underground from some time.
I did fear how the day might unfold.
I parked my car just a few hundred yards away and heard a thunderous boom echo down the road. I didn't know it then but it was blast that ripped the roof off a double decker bus.
At King's Cross the professionalism and control of the emergency services was impressive, and the mood was one of calm, as if they'd managed to suck the terror out of terrorism. If yesterday was about the euphoria of winning the Olympic Games - today is about the horror of losing so many lives in Central London.
But if this was the work of al-Qaeda trying to terrorise Londoners, my impression from King's Cross is that they failed.
David Shukman : In the air over London : 1750 BST
We're on the very edge of an air exclusion zone which has been imposed over most of London. From here you do get an extraordinary sense of how the city has been wounded, but is very slowly recovering in certain ways.
Commuters are struggling to get home tonight
We've flown over gridlocked streets, and streets where the traffic is moving normally. Quite comforting to look at major landmarks like Tower Bridge and see how much is intact despite this morning's ghastly events.
I can see Liverpool Street station and trains that are starting to move. And below me the river boat service, for which people are queuing to use. The river is probably one of the very few ways home.
To the south I can see the Dome, a venue for the Olympics. There will now be a lot of questions about the Olympics after today's events.
Shaun Ley : Downing Street : 1745 BST
Mr Blair has quite clearly said he believes this is the work of some kind of Islamic terror group. He was very clear in saying that the values of that group are very different from the values held by most muslims.
Jane Hughes : King's Cross : 1720 BST
The roads are almost empty with no cars, but the pavements are jammed. People have realised that they are not going to get home unless they walk.
I spoke to a construction worker employed at King's Cross station, and he said he spent all day under ground helping carry out casualties and administer first aid.
Now the logistical question is what happens to all the people who were going to use this station to get home. It's going to be some time before the network starts again, because every bus, train and station now has to be physically searched before they can start running again.
Dominic Casciani : Royal London Hospital : 1715 BST
The evening commute home from the City of London has began in a way that people have not seen before.
Hundreds and hundreds of city workers are walking the length of Whitechapel Road, packing the pavements, because there is no other way they can leave their offices.
The A-Z map of the capital is fast becoming ubiquitous - but it is strange to see so many Londoners carrying them, not knowing how to make their way home on foot.
Public transport is still not operational in this part of London - many shopkeepers have accepted that there's no point in remaining open today. Schools and shops have pulled down the shutters already and there's a general sense of quiet gloom on the roads.
In fact the only places doing any business at all are the East End pubs which are all full of people quietly watching the live news coverage of the events.
Anyone who knows and loves this part of London loves it because of the sheer amount of activity and noise which makes it a unique place, but today London's East End has become a very, very sad place indeed.
Marie Jackson : Marylebone : 1710 BST
I walk the 90-minute journey from Aldgate East back to BBC London's Marylebone office, against the crowds of workers weaving their way through the city.
Many are heading towards Fenchurch Street and Liverpool Street stations as rumours circulate they are both open. Others wander with print-outs of street maps planning to make their entire journey on foot.
The sun is out giving a sense that the horrors of the bleak rainy morning may be over. Londoners stop to talk to each other about their experiences.
Glenda Cann was halfway down an escalator towards Liverpool Street's Central Line when commuters were told to evacuate.
"As we got out, it was mayhem," she says. "The air was hazy. People could smell smoke and you could hear all the sirens."
Moments later Thomas Bullock, a stallholder, was in Red Lion Square when he heard the explosion in Russell Square.
"As we were eating breakfast we heard a bang. It sounded like a building being blown up. We walked outside and could see policemen running towards Russell Square carrying first aid boxes."
Helen Bart : Euston Road : 1700 BST
What a contrast to this morning.
There are now many people out walking and catching their trains home. A couple of hours ago this road was completely cordoned off and you could have heard a pin drop.
I spoke to a nurse earlier from the University College hospital who said everyone has been pulling together and that there was a very calm atmosphere as staff got on with their work.
Trying to get to work this morning I found myself at a pub in Kings Cross where the landlady was giving out free cups of tea and people were buying drinks; doing anything they could.
Everyone was trying to help each other out.
I'm a Londoner born and bred but I've never seen anything like this - it was fantastic to see everyone pulling together.
Chris Eakin : BMA Headquarters, Tavistock Square : 1655 BST
It's not entirely true that everything has stopped in central London. Although the transport has halted, there are still people going about their business, even shopping. But more people are walking.
A GP here has described how ten wounded people were taken into the courtyard here, and were treated by a group of doctors whose meeting had just broken up. It's a very strange scene this evening.
Gordon Corera : BBC Television Centre : 1630 BST
The finger must point at al-Qaeda, though that doesn't mean it was them. We haven't had any official confirmation. But it you look at the timing - the G8 summit - and the method - simultaneous attacks, a very typical al-Qaeda method.
Those kind of things do indicate us towards al-Qaeda. We don't know if these were suicide bombs or packages left on trains. Both of these methods have been used before.
Two people are known to have died on the bombed bus
After the general election there was a slight lowering of the threat level from international terrorism. There was still a concern over terrorism, but perhaps less sense of an imminent attack.
And there has to be a certain amount of concern that something else could happen. We can expect security to be tight around the country as a result of this.
Alison Freeman : Hyde Park : 1615 BST
Many of the shops in Oxford Street are closed with signs telling customers "Due to the events of 7 July, this store is closed" and armed police patrol the streets surrounding the US embassy.
Walking through Hyde Park I am joined by hoards of commuters beginning their long journey home as streets remain devoid of buses and the Tube network closed.
Dominic Casciani : Royal London Hospital : 1540 BST
It's a sad fact of life that faith leaders in the East End have been preparing for the fallout of terrorism in London.
The Bishop of Stepney, Stephen Oliver, and Dr Mohammed Abdul Bari, the chairman of the East London Mosque, have just spoken together outside the Royal London Hospital saying the East End and the whole of London must remain united in the face of terror.
Jane Mower : St Mary's Hospital : 1530 BST
Even though the cordons have begun to come down, any attempts to walk around are hampered by continuing security alerts.
A police officer directs people away from the site of yet another suspect package. Hastily written sign in Starbucks' windows tell customers "sorry we are closed".
Police sirens draw anxious stares as people tentatively try to go about their business. Meanwhile TVs in pubs and cafes are tuned to the news.
And even a teenager is distracted from her magazine as Tony Blair makes an announcement.
Gordon Corera : BBC Television Centre : 1455 BST
There is still nothing confirmed regarding responsibility, and I don't think we should expect anything to be confirmed for some time while the attacks are being investigated.
Emergency services are still at central London stations
But the indications, from the timing and the method, the nature of the attack and the lack of warning, are clear.
The most worrying trend has been the way al-Qaeda has fragmented.
At first people thought that was a good thing, because that meant a sign of its defeat, but lots of groups have popped up in other countries which are inspired by them.
Frank Gardner : BBC Television Centre : 1445 BST
At the moment the only claim for responsibility comes from a group calling themselves The Secret Organisation Group of Al-Qaida of Jihad Organisation in Europe. It's not a name anybody has heard of before.
It's a 200-word text calling on people to rejoice because it's time to take revenge on the British government for what it calls the massacres Britain is committing in Afghanistan and Iraq.
It goes on to call it a blessed raid in London and that Britain is now burning with fear and panic. Finally it warns Denmark, Italy and all the crusader governments that they'll be punished too if they don't withdraw their troops from Iraq and Afghanistan.
But we don't know yet if it's genuine.
Marie Jackson : Aldgate : 1710 BST
Arriving at Aldgate East, three police officers on horseback barricade Fenchurch Street. There is little activity now beyond the police tape, just a growing band of journalists and television crews kept outside.
Pedestrians seem less bothered than usual by the rain. Many are happy to get wet safe in the knowledge that friends and family are safe.
"The first I realised was as I was coming into work," said Heather Carson, who works in a solicitors office in Fenchurch Street, yards from the Aldgate East explosion.
"We were told there was a security alert on the tube and then we were told that Bank was shut because of a power surge.
"We knew when we got off because the streets were very quiet and there was loads of sirens going off."
Dominic Casciani : Royal London Hospital : 1415 BST
Whitechapel Road is strangely quiet - at any time of day or night it's a frenzy of activity, thanks to one of the largest street markets in London. But today police cordons restricting traffic coming anywhere near the explosion site at Aldgate mean an entirely different atmosphere has descended on the East End.
Clearly the emergency operation is still running at full pelt. Only seconds ago another blood bank convoy dashed down to Aldgate Station at 60 miles per hour.
We don't know exactly what's going on at the station, and whether people are still trapped underground, but the hospital is updating its figures for how many people it's treating.
As of 1345 Royal London Hospital dealt with 208 casualties, 26 of which had been admitted. At the moment 13 are being operated on and three are in intensive care.
Marie Jackson : Fenchurch Street : 1345 BST
My destination is Aldgate East, scene of one of the morning's explosions. But as is happening all across London, roads are becoming no-go zones as suspect packages are uncovered.
There have been hundreds of walking wounded
At the junction of Gracechurch Street and Fenchurch Street the police tape goes up, officers redirect traffic and the usual lunchtime haunts of M&S and Boots are evacuated. Sniffer dogs and police vans are quickly at the scene but within minutes the package is investigated and dealt with.
Officers re-open the road as shop staff gather under shelter from the rain, talking about how are they ever going to get home.
Dominic Casciani : Aldgate East : 1325 BST
Workers in the city of London are still trying to take in what has happened. And almost every pub around Liverpool Street is packed with people wanting to watch the One o' clock news.
At the East India Arms, a small pub on Fenchurch Street, bankers quietly sipped their pints of Young's bitter while listening to the news and watching the pictures of how their city has been changed.
Those in the pub were recounting tales of the morning's events, some of them speculative, much of it rumour.
When the prime minister's statement came up on the news the pub almost immediately fell silent.
However, the strange thing is that despite this terrible attack, there really is an air of people just trying to get on with things. As soon as the prime minister stopped talking, the pub erupted in conversation with all the usual talking points - contracts, deadlines and projects.
June Kelly : Edgware Road : 1310 BST
The police have confirmed there have been a number of fatalities at Edgware Road.
A number of people have been seriously injured, and then there are the walking wounded. Police say everyone is now out of the tube station.
Two trains were caught up in the explosion here. Witnesses have spoken about glass showering down on them and being plunged into darkness.
People who got out are very shaken and have told us in dramatic detail about getting out, but the very bad news is that some people have died here.
Jane Mower : St Mary's Hospital, Paddington : 1300 BST
Workers are starting to come out of their offices for lunch breaks and are standing around trying to absorb what is going on around them.
One woman told me how she struggled to get into work only to be told the building had been evacuated and she was being sent home.
Another talked frantically into her mobile, trying to track down a family member she has not been able to get in touch with. It is all cordoned off around here - there's no traffic at all.
Gordon Corera : BBC Television Centre : 1248 BST
It could be that a number of different statements of responsibility appear on the web in web chat forums that militant groups use.
A lot of people did think the core al-Qaeda leadership had been severely damaged.
But the worry has always been that there were groups influenced by them, who believe in the same thing and follow the same model.
Doctors arriving in central London
That was the model for the Madrid attacks last year. They were not people who were centrally commanded, directed by Bin laden in a cave.
In a way those groups are harder to direct and stop than those travelling out of Afghanistan or who are in contact with the leadership left there.
Alison Freeman : Edgware Road : 1245 BST
There are hordes of press here but it's difficult to contact the office because the phone networks are down. The whole area is cordoned off and there are crowds of people at the cordons.
There are several fire engines and ambulances coming in and out all the time, although I haven't seen any injured people. At St Mary's Hospital there are staff standing outside waiting for people to come in - there is a constant stream of fire engines, but it is quite calm.
Ben Davies : Tavistock Square : 1241 BST
I have just cycled across central London which has been hit by major road closures with few vehicles about except ambulances and police vans.
Near the scene of the Tavistock Square bus attack Euston Road is shut as is nearby Russell Square.
My route took me from Bloomsbury via Soho and Trafalgar Square to the BBC Westminster offices. The normally bustling West End is eerily quiet apart from people trying to get to work and the odd determined tourist.
In Tavistock Square the wreckage of the roofless red London bus sits outside the offices of the British Medical Association, newspapers blowing in the road. A symbol of an ordinary Thursday morning commute cruelly interrupted.
Andrew Winstanley : Liverpool Street : 1239 BST
The station is still closed and all the shops are being closed with people still inside; there seems to be a general lockdown.
Police are going from door to door searching apartments above shops to check them out. There is concern that there may be more undetected devices.
Jeff Randall : City of London : 1235 BST
There are lots of men in suits coming out of the City of London - clearly they couldn't leave their offices and get on to the tubes and taxis so they're simply walking home - it's an extraordinary sight.
The emergency services are really rallying the troops. As I battled in from Essex ambulances and police cars were pouring in from Essex to try to shore up the job the emergency services are doing here. As for the City itself, trading is remarkably calm. There's a very low level of trading largely because many of the big banks have evacuated their offices.
Fergal Parkinson : Tavistock Square : 1220 BST
I'm outside the British Medical Association on Tavistock Square where a lot of the injured are still being treated. People are lying on the ground being treated by paramedics and doctors - some of whom obviously work at the BMA.
Five ambulances have arrived and are taking a few more people away as well. There's also a large ambulance with seats on board and people are starting to walk on to that vehicle. I've also seen blood supplies arrive - three vans from the National Blood Service with blue lights flashing.
Dominic Casciani : Aldgate East : 1215 BST
At Aldgate East witnesses to the scene said they saw the best side of the emergency services shortly after the incident happened.
St Botolph's Church has become some kind of command centre as it's close to the Tube exits.
Meanwhile at the cordon blood bank couriers have been seen taking supplies to the scene on mopeds so they can get round the chaotic traffic in the city.
One of the strangest scenes has been a queue of helicopters just to the east of the station waiting to land on the helipad at the Royal London Hospital.
Things have quietened down a lot since then - the mobile phone network is back up which means the long queues which had formed at public phone boxes have all gone.
Guto Harri : BBC Television Centre : 1210 BST
Tony Blair has talked on many occasions about what keeps him awake at night. And it seems that his worst nightmare is now happening. In his statement he was very calm and determined, saying he was going to return to London. He wants to speak to the people who have suffered, and actually try and get to grips with the situation.
There are well established procedures in place. Which is why we're seeing all these emergency procedures being put in place, such as transport being shut down. They have been preparing for this.
John Pienaar : Gleneagles : 1209 BST
The first confirmation that these are being treated as terrorist attacks and the prime minister is sending two messages - firstly of course of sympathy for the victims, and secondly a message of defiance to the terrorists.
The visible evidence is that he will return to London in a couple of hours to be briefed by senior officers and then return to the G8 summit later to carry on.
All leaders seem to have decided not to give the terrorists what they were looking for - the cancellation of the summit.
Peter Hunt : Liverpool Street : 1205 BST
People here really are struggling to resume their working lives and there are lots of people standing around in huddles - there's little appetite for work. Others are trying to make their way by foot as it is impossible for them to make their way by any other means within the City of London.
Firemen help the injured at Aldgate East underground station
Large numbers of streets and roads are closed. I passed 12 London buses who'd been advised not to move. The emergency services are trying constantly to stop people from hanging around near the cordon - quite extensive forensics work is going on on the underground well away from prying eyes.
Dominic Casciani : Aldgate East : 1200 BST
It's midday in what should be one of the busiest parts of the city, but all the areas surrounding Aldgate East have been cordoned off, leaving city office workers trying to make head or tail of what is going on.
At the Minories entrance to the cordon, eight London firefighters have just left the scene, covered in grime and looking pretty exhausted.
But for anyone on the outside of the cordon it is very difficult to know what is really going on as the London security plan swings into action.
Jim Wheble : Aldgate : 1159 BST
There have been a lot of ambulances coming up and down to Aldgate. Looking up from street level, I saw six or seven army officers in fatigues surveying Liverpool Street with binoculars from the rooftops.
Offices have been evacuated around Aldgate, with people coming out of their offices and not knowing what is going on. The situation here is a lot more controlled now.
Mark Easton : Kings Cross : 1155 BST
The situation has been developing over the last couple of hours. When I arrived just after 9am I saw some people, walking with now familiar black faces and arms. Since then the situation has developed rather dramatically.
There are 4 double decker buses being used as treatment centres for the less seriously injured. I must have seen 60 or 70 people brought up, many in tears, some with lacerations to their faces. One man was hobbling, another woman in a wheelchair with a very badly injured leg.
Richard Foster: Liverpool Street: 1135 BST
Hounsditch is sealed off and there are police on horseback there. Liverpool Street station is sealed off. The number of people there was in its thousands when I first arrived, but now it has thinned out. The pubs are full round here; people are gathering for news updates and sending texts to let people now they are alright.
Nick Thatcher : Royal London Hospital : 1130 BST
The Royal London Hospital have been receiving casualties all morning. This is a major hospital in East London. There's an air ambulance landing on the roof behind me. There are buses behind me which have come from the Kings Cross area in central London. On board are walking wounded who have been ferried here.
Jon Brain : Edgware Road : 1115 BST
There's been a scene of chaos and confusion all morning here but it's beginning to settle down. The entire area around the tube station has been sealed off and there are dozens of emergency vehicles here.
We've seen a number of walking wounded emerge from the station, many of them covered with blood and obviously quite distraught. They are being treated at a hotel opposite the tube station.
The concern now is whether there are still people trapped inside the tube station underground. I've seen a team of paramedics go into the station in the last half hour.