Elizabeth line passengers face severe disruption on journeys between Paddington and Heathrow Airport after a track fault.
Travel between Paddington and Heathrow Terminal 5 will see delays and cancellations after a broken track is forcing trains to run slower than usual. Heathrow Express and Great Western Railway trains are also affected.
While Network Rail engineers are monitoring the fault, issues are expected to last until the end of the day.
Elsewhere on the London Underground, a stretch of the Piccadilly line is suspended between Rayners Lane and Uxbridge due to poor rail conditions caused by falling leaves.
In other traffic news, the M5 was closed in both directions in Somerset after a 17-year-old girl was killed in a crash. She was hit by a car on the motorway after getting out of the back of a police car.