Emergency crews are handling an incident that has led to the shutdown of several rail routes serving Heathrow Airport, the nation's largest airport.
The outage affects the Elizabeth line, Heathrow Express and Great Western Railway, with every line between London Paddington and Heathrow Terminals as well as Reading now closed.
Passengers on the Elizabeth Line are being told to take bus links from Hanwell to West Ealing, heading toward Ealing Broadway or Southall.
National Rail warns that the disruption may last until at least 12:00 pm.
The incident was reported on the tracks just before 8:00 am.
Tickets remain valid on London Underground, London Buses, Southwestern, Thameslink, DLR, South Western Railways and Chiltern Railway services.
Travelers departing from central London can still use the Piccadilly Line on the Underground.
Authorities advise allowing extra time to reach the airport.
National Rail's website states: "The emergency services are currently dealing with an incident between London Paddington and Heathrow Terminals / Reading. So that they can safely carry out their work, some lines have been closed. Trains operating between these stations may be cancelled, delayed by up to 60 minutes or revised as a result. Major disruption is expected until 12:00."
Additional problems are reported between Weybridge and Surbiton.
South Western Railway posted on X: "A speed restriction over defective track is affecting the railway between Weybridge and Surbiton. Trains may be cancelled, delayed or revised because of this problem."
