London Paddington train delays refunds offered
Passengers are facing severe disruption on services between Reading and London Paddington due to overrunning engineering works.
A First Great Western (FGW) spokesman said a "very limited" service was running, although FGW's website earlier said no trains were getting through.
Passengers who choose not to travel have been offered refunds or can use the tickets on Sunday instead.
Most services into Paddington are being stopped at Reading.
Customers are allowed to use their tickets on South West Trains' service to Waterloo.
Network Rail said disruption was likely to last until at least 19:00 GMT.
An FGW spokesman said the problem lies with only one line, instead of two, being open and rolling stock in the wrong position.
He added a section of the line had now been handed back to FGW but it would be some time until trains were back on track.
Passengers travelling between Oxford and Paddington are advised to travel with Chiltern Trains via Marylebone.
Trains between Paddington and Greenford and the local service between Paddington and Hayes and Harlington are currently unable to run.
FGW said it would post updates on its website.
It comes after all trains to and from London King's Cross were cancelled for the same reason.
The Office of the Rail Regulator is to launch an investigation into the disruption.