Commuters heading to London are warned they face major disruption throughout Wednesday - there are no services into Paddington beyond Reading due to overhead line problems.
Trains are unable to run between London Paddington and Slough or Heathrow Airport after overhead electric wires were "severely" damaged near Ealing.
Many trains are currently stranded between Paddington and Reading due to a loss of power supply.
Network Rail said it expected to open two of the four train lines by midday, but warned disruption would last until the end of the day. Travellers are being advised not to travel unless absolutely.
Great Western Railway says a reduced timetable would impact most mainline routes to and from Paddington.