'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'.
Passengers attempting to travel between London and Slough are advised to avoid the station until at least midday.
A Network Rail spokesperson said: "Extensive damage to 500 metres of overhead electric power lines last night means no trains have been able to run between London Paddington and Reading and Heathrow this morning".
No trains are running in or out of London Paddington this morning after disruption which started overnight.
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The incident happened exactly one year after the first of the Class 800 trains to enter GWR service suffered leaking air conditioning and a 41-minute delay on its inaugural journey with senior politicians and rail bosses on board.
The train operator added: "Starting and terminating at Reading, an hourly train service will operate between Reading and Swansea in each direction".
A spokeswoman said: "We are experiencing severe disruption on all services into and out of London Paddington and this is likely to affect services in other areas for the rest of the day. No one is held to account for poor service", she said.
Mitch Riviere, who works for HMRC, told the Press Association: "I was thinking of trying to go via Waterloo but that's not a great option - but it might have to be that or walk there". However, there'll be "a small number" of cancellations or alterations during the evening peak period.