Paddington station was shut this afternoon with dozens of services hit by cancellations.
Passengers were told all services to Reading and the west country were not running after a person was hit by a train at Hayes and Harlington.
Disruption was expected on Great Western Railway, Heathrow Express and TfL Rail services until 6pm.
Most services between Paddington and Slough or Heathrow Airport have also been severely delayed or cancelled.
Great Western Train services are still running between Paddington and Hayes at Harlington.
For TfL Rail passengers, tickets will be accepted on the London Underground and London buses.
Meanwhile, Great Western Railway said its customers can use their tickets on London Underground services via any reasonable route, South Western Railway services between Waterloo and Reading, and Chiltern Railways between Marylebone and Oxford.
