First Great Western rail disruption from Swansea, Cardiff
Rail passengers travelling to and from south Wales and London have faced disruption after engineering works overran.
First Great Western (FGW) has said mainline services have not been able to run in or out of London Paddington.
Passengers have been diverted via Reading or onto the Underground via Ealing Broadway due to cancellations.
The number of trains have been reduced to an hourly service because of engines stuck at the depot in London.
A FGW spokeswoman said: "This is set against a background of problems with overrunning engineering works in the network.
"We have been running an emergency timetable - this has meant one train an hour from Swansea and Cardiff where there would usually be two."
One passenger Hilary Cameron, travelling from Newport on the 10:39 GMT with her brother to London, said there had been "chaos".
"You can't move, there are people having to stand right through the aisles with their luggage," the 66 year old said.
"We haven't been told a thing. It's dangerous, if there was an incident it could be carnage - no-one can move."
She later said the service stopped at Reading and passengers were waiting to find out how to get to London.
FGW said passenger safety was the "number one priority" and trains were able to cope with passengers standing.
Meanwhile, refunds were being offered to those who chose not to travel.