The driver of a tram which derailed killing at least seven people and injuring dozens more has been arrested.
Emergency services were expected to continue work late into the evening at the scene near Sandilands tram stop in Croydon, south London.
Deputy Chief Constable Adrian Hanstock said: "We expect to be at the scene for at least the next 24 hours, continuing searches and carrying out forensic examinations in support of the investigation into the circumstances, and in order to provide a report for the Coroner.
"Tomorrow, we will assess how and when it is appropriate to recover the tram and remove it from the tracks."
More than 50 people were injured when the crowded rush-hour tram tipped on to its side next to an underpass near the stop shortly after 6.10am on Wednesday.
A spokeswoman for London Ambulance Service confirmed eight people have serious or life-threatening injuries.
The tram had been travelling at a "significantly higher speed than is permitted" when it derailed, according to the independent Rail Accident Investigation Branch said.
At least five people were trapped and had to be freed by rescuers, with the London Fire Brigade saying earlier they had sent eight appliances and more than 70 firefighters to the scene in Addiscombe Road.
Prime Minister Theresa May said her "thoughts and prayers are with all of those who have affected by this terrible incident on the tram in Croydon".
The incident is believed to be the first tram crash involving fatalities on board since 1959, when two women passengers and the driver died after a tram caught fire in Shettlestone Road, Glasgow, following a collision with a lorry.
Accident investigators have gone to the scene to probe how the derailment happened.
London Ambulance Service said: "We have treated a number of patients and over 50 have been taken to hospital."
People living nearby told of hearing a loud noise and seeing the injured being carried off on stretchers.
Croydon resident Hannah Collier, 23, said: "I heard a massive crash at about 6.15am, then heard shouting, then the emergency services arrived.
"They started bringing up the casualties, some very seriously injured. People were carried away on stretchers."
A Transport for London (TfL) spokesman said: "We are currently working with the emergency services following a derailment involving a tram in Croydon.
"There is currently no service on the tram between Reeves Corner and Addington Village / Harrington Road. We will give further information as soon as possible."