Millions of people across the UK and Europe have observed a three-minute silence on Wednesday to remember the 150,000 killed by the Asian tsunami.
Londoners were among millions in the EU who paid their respects
The silence started in Britain at 1200 GMT, but was held across Europe one hour earlier.
Tony Blair has predicted the British Government will eventually give "hundreds of millions" of pounds in aid to countries hit by the tsunami.
It was his first public comment since returning from his holiday in Egypt.
Mr Blair told BBC Radio 4's Today programme that he had been "intimately involved" in "all decisions at all times" despite being abroad.
Across Europe, people paid their respects by observing the silence at 1100 GMT.
The German stock exchange, in Frankfurt, stopped trading, while cars remained motionless in the streets of Stockholm, Sweden, and mourners stood shoulder to shoulder in Paris.
Mr Blair observed the silence in private at Downing Street.
Chancellor Gordon Brown joined Welsh First Minister Rhodri Morgan to mark the remembrance in Cardiff.
In the UK, flags flew at half mast on government buildings and at Buckingham Palace.
The royal household also observed the silence, a Palace spokeswoman confirmed.
Britons paid their respects after pledging £76m to the Disasters Emergency Committee (DEC) to assist victims of the tsunami.
The DEC, an umbrella group of 12 British charities, said public contributions to its appeal would eventually top £100m, not including direct donations to individual organisations.
The Charity Commission, which regulates charities in England and Wales, publishes guidelines on Wednesday aimed at ensuring as much money as possible reaches the victims in Asia.
The guidelines include advice to people running collections about avoiding duplication and bureaucracy and on allowing charities to make the most of all tax breaks available.
The government has so far allocated £50m in aid to the affected countries, but has promised to match the amount raised by the public.
Be aware of available tax breaks
Don't duplicate what other groups are doing
Bank all cash as soon as possible
Report back to those who have donated so they know the money is helping
The Charity Commission
It also announced it has offered to send 120 Gurkha troops to Indonesia to help in the relief effort, although this offer was later politely refused.
Discussions have begun with Indonesia on the exact timing and location of the deployment.
However International Development Minister Gareth Thomas said the offer was aimed primarily at Aceh province, the area closest to the epicentre of the earthquake that triggered the devastating tsunami.
The three-minute silence was suggested by the Luxembourg EU presidency last week.
Mourners in Paris respected the three-minute silence at 1100 GMT
UK Culture Secretary Tessa Jowell said: "This is to commemorate the victims of the catastrophe in south east Asia and is in solidarity with the people of the affected countries.
"The government hopes employers will do all they can to ensure employees are able to observe the silence and pay their respects at that time."
Television services on BBC One, Two and News 24 observed the silence together with the corporation's main national radio stations.
The London Stock Exchange observed the silence
Birmingham New Street station marked the event
Bristol's Cribbs Causeway shopping centre fell silent
Worshippers congregated at Oldham's Buddhist temple
Also on Wednesday, prayers will be said at churches, cathedrals and other places of worship throughout the UK.
A spokesman for the Church of England said the silence would give people of all religions the opportunity to grieve for both the victims of the earthquake and those left homeless.
The tradition of collective silences had begun with Armistice Day, a year after the end of World War I, he said.
He added that the public's response to a silence after the 11 September 2001 disaster showed they remain relevant and effective in the modern era.
Jeremy Bowen presents The Killer Waves - A Real Story Special - on BBC One at 2100 GMT on Thursday 6 January.