Trains to and from London Paddington station have been suspended after a person was hit by a train.
The incident took place on the line between Heathrow Airport and Paddington at around 7.30pm this evening.
Great Western Rail tweeted on Friday evening: "Due to a person being hit by a train between Reading and London Paddington, all lines are currently blocked
"London underground are accepting GWR ticket via any reasonable route.
"SWR are accepting GWR tickets between Waterloo, Windsor and Reading".
Heathrow Express has also been affected by the incident.
It tweeted around 9pm that lines had reopened and service were resuming with departures every 30 minutes.
Just before 9.30pm, all lines between London Paddington and Southall had reopened.
Disruption is expected until the end of the day.
Transport for London said there were severe delays between Paddington and Reading/Heathrow all terminals due to the incident.
It added that there was good service between Liverpool street and Shenfield.
Disruption to and from London Paddington is expected until 10pm on Friday night.
