No trains are running in or out of London Paddington this morning after disruption which started overnight.
National Rail said overhead electric wires were "severely damaged" on Tuesday evening, stopping trains running in and out of the west London hub.
It's affecting the Heathrow Express, TfL rail, and Great Western Railway services.
Network Rail engineers are working to fix the damaged lines and to recover stranded trains, and hope to have two of the four lines working again by midday.
However there will be disruption all day.
TfL rail services are suspended until at least 2pm, and a rail replacement bus service is operating between Paddington and London Heathrow.
Heathrow Express customers can use the underground service.
Great Western Railway services will mostly be starting and terminating from Reading, with a reduced service between there and Slough.
The operator said: "Owing to the extent of the damage, no trains are expected to be able to operate between London Paddington and Hayes & Harlington in either direction for much of Wednesday.
"As a result, GWR, TfL Rail and Heathrow Express will not be operating a train service between London Paddington, Hayes & Harlington or Slough until such time as repairs have been completed."
Customers are advised not to travel between Paddington and Slough. People coming into London from beyond Reading are asked to get to Waterloo, Marylebone or Euston, and not London Paddington.
Great Western Rail customers can use their tickets on a variety of other services and are urged to check before they travel.
It comes after passengers reported hours of disruption on Tuesday evening, with some facing journeys of three hours to get home.
Matthew Benjamin tweeted about "chaotic scenes" at Reading, and said he'd had to queue in an underground car park for a taxi to get back to London, where he had two night buses ahead of him.
He added: "No senior @GWRHelp management or Reading Station staff in sight and more junior GWR staff trying their best to coordinate and organise confused, tired and angry passengers."
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Others said they were advised by staff at Great Western Railway to arrange a place to stay in London, after the lines closed on Tuesday.
Anyone facing disruption may be able to claim compensation.
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