Rail services at London’s Paddington station were suspended after a person was struck and killed by a train.
British Transport Police (BTP) said they received a report about the incident near Iver station in Buckinghamshire at around 7.15am on Thursday.
All lines between Paddington and Reading were blocked, causing major disruption to Great Western Railway, Elizabeth line and Heathrow Express services.
Some lines were reopened by 10am but delays and cancellations continued.
Paddington is the UK’s second busiest railway station.
A BTP spokesman said: “Officers were called to the line near Iver railway station at around 7.15am today following reports of a casualty on the tracks.
“Paramedics also attended; however, sadly, a person was pronounced dead at the scene.
“The incident is not being treated as suspicious and a file will be prepared for the coroner.”
GWR said in a statement: “It is with great sadness that we report a person has been struck by a train.
“Some lines have now reopened to allow the movement of trains once again but it will take a while to reintroduce a full service.
“Until that is in place, where we can, we will divert trains to run on other lines around the affected area.
“There may be certain instances of trains being held at stations some distance from the incident.
“This is due to congestion and such action will avoid any trains becoming stranded in open country.”
Disruption is expected to continue until 11am.
GWR said: “It is with great sadness that we report a person has been struck by a train, leading to all lines being blocked.
“It is necessary to bring all trains in the affected area to an immediate stop.”
London Paddington was closed for engineering work for the previous four days.
It was repeatedly affected by infrastructure faults in the preceding weeks.