Train services have been cancelled or delayed due to a grass fire near a train track in the London Paddington area.
National Rail said the blaze caused an electricity supply failure, which left all lines between Paddington and Heathrow Airport and Reading blocked.
Cancellations and delays to services are expected until the end of the day.
Passengers travelling towards Heathrow Airport will need to use the Piccadilly line, or local and London buses.
London Fire Brigade said six fire engines and about 40 crew members are tackling the blaze near Scrubs Lane, North Kensington, where it was called at just after 4.10pm on Saturday.
Crews from Hammersmith, Paddington, Ealing and surrounding fire stations have been sent to the scene, it added.
Great Western Railway (GWR) services to Reading have been cancelled, while the Elizabeth line is part-suspended.
No trains are running in either direction between Paddington and Heathrow, the Heathrow Express said.
The airport advised passengers to leave extra time for their journeys, adding that the Piccadilly line, which runs services to the airport, is also experiencing delays.
Transport for London (TfL) said the Elizabeth line is suspended between Paddington and Heathrow terminals four and five, and between Paddington and Reading, while the line to Abbey Wood is experiencing severe delays.
There are severe delays across the entire Piccadilly line due to an earlier trespasser at Hammersmith, according to the TfL website.
Those on the Elizabeth line are advised to “seek alternative routes to complete your journey if you are travelling west of London Paddington. Services will only run between London Paddington and Abbey Wood / Shenfield. Some trains may be diverted to start from London Liverpool Street.”
GWR said trains may be cancelled, delayed or terminated at and started back from Reading. Tickets for today will be valid for travel on Sunday at no extra cost.
