Rail services to and from East Croydon station have been diverted following an incident on the tracks on Tuesday evening.
Commuters are being urged to delay travel to the busy south London station until later, with warnings that alternative routes could extend journey times by around an hour.
Major disruption is expected until 9pm, National Rail said.
“Lines have reopened between East Croydon and Purley following the earlier incident where a person was hit by a train,” it said in an update.
“Trains running between these stations may still be cancelled, delayed by up to 45 minutes or revised.”
Thameslink told passengers in an update: “It is with great sadness that we report a person has been hit by a train at East Croydon. All lines are blocked between these stations whilst the emergency services work to deal with this incident.”
Services will not stop at East Croydon until further notice, Thameslink said.
“You will need to use an alternative route if you are travelling to this station,” it warned.
“Trains that usually run between London Bridge and East Croydon will instead run between London Bridge and Selhurst.
“All trains which run to and from London Victoria will also stop at Selhurst, and all trains from London Bridge will also stop at Norwood Junction.”
Tickets are being accepted on the Tube, buses, trams and the Overground as well as Southeastern services, Southwestern services between Southampton/Portsmouth and London, and alternative Southern and Thameslink services.
British Transport Police has been approached for comment.
