A woman believed to be in her 30s and a three-year-old boy died when they were struck by a train during Friday morning rush hour.
British Transport Police were called to the incident at Riddlesdown rail station near Purley, south London, at around 8.20am.
Ambulance teams and Met Police officers also attended and the woman and child were declared dead at the scene.
The station was temporarily closed while the emergency services dealt with the incident and the police investigation was carrying on.
The line between Uckfield/East Grinstead and South Croydon reopened early this afternoon but delays are expected until around 4pm.
There was considerable disruption to services run by the Southern train company in the area, with buses running between some stations and extended journey times.
British Transport Police senior investigating officer Detective Chief Inspector Simon Taylor said: "Our thoughts remain with the family and friends of the woman and child involved in this tragic incident.
"Officers are continuing to work to establish the full circumstances surrounding this incident, although early indications show that no-one else was believed to have been involved."
Mr Miller said: "Our thoughts remain with the family and friends of the woman and child involved in this tragic incident.
"Officers are continuing to work to establish the full circumstances surrounding the incident although early indications show that no one else was believed to have been involved."