Trains to and from Heathrow Airport have been halted after a trackside grass fire caused delays and cancellations.
National Rail said “major disruption” was expected until the end of Saturday following the incident which began shortly after 16:00 BST.
A statement said all lines were blocked between London Paddington station and Heathrow’s terminals, as well as Reading, due to “a failure of the electricity supply caused by a fire next to the track”.
It comes hours after a separate grass fire on Heathrow’s airfield shut a runway earlier on Saturday.
Pictures on social media showed crowds of stranded passengers at Paddington, one of London’s main rail hubs.
London Fire Brigade said six fire engines and around 40 crew members were tackling the blaze near Scrubs Lane, North Kensington.
Great Western Railway, external cancelled its services to Reading and no Elizabeth line or Heathrow Express services were running between Paddington and Heathrow on Saturday night.
The airport advised passengers to leave extra time for their journeys, adding that the Piccadilly line, which runs services to the airport, also has delays.
Earlier on Saturday, Heathrow’s southern runway was closed while crews tackled a grass fire on the airfield.
It caused some disruption with at least two flights diverted elsewhere. Heathrow apologised for any disruption and said the fire was extinguished quickly.
That comes weeks after another grass fire near Heathrow’s southern runway which forced 18 flights to divert and destroyed a large area of grassland.
While weather has cooled across much of the UK in recent days following record-breaking heat over the summer, fire crews have still been warning of wildfire risks.
The Met Office’s Fire Severity Index, external shows that if a wildfire was to occur, it would have a “high” fire severity in most of south-east England and some of the Midlands.
The fire severity is “exceptional”, the highest level on the index, in some parts of London including Heathrow, as well as on the Essex and Suffolk coasts.