Three people have died after being struck by a train.
British Transport Police (BTP) were called to Loughborough Junction station, near Brixton in south London, at 7.30am on Monday.
They described the deaths as “unexplained”.
Officers remain at the scene, where they are working to identify those killed and inform their families.
A “number of inquiries” are being carried out by BTP to establish how they came to be on the tracks.
Detective Superintendent Gary Richardson said: “My team are now working hard to understand what happened and how these three people came to lose their life on the railway.
“My thoughts are with the family and friends of these three people.
“At this time, we are treating their deaths as unexplained as we make a number of immediate inquiries.
“I would ask anyone who was near to Loughborough Junction this morning, and saw something which they think might be relevant, please contact us as soon as possible.”
It is understood that spray cans were found near the bodies of the three people.
Sources told the Press Association that the incident could have happened overnight, when freight trains run, as the bodies were not spotted until around 7am.
Freight trains carry out a lot of the infrastructure work on Britain’s railways, usually overnight when the passenger pathways are clear.
A Network Rail spokesman said: “Network Rail is assisting the British Transport Police as they investigate an incident at Loughborough Junction this morning.”
Rail regulator the Office of Rail and Road has opened a preliminary investigation.
Loughborough Junction is an elevated station managed by Thameslink and located on a line between Herne Hill and Elephant and Castle stations.
It is near three other lines used by trains which do not stop at the station.
The station is open but BTP warned that services will be delayed while the scene is investigated.