Five people were killed when a London tram derailed and tipped onto its side, police said adding the driver has been arrested.
More than 50 people were taken to hospital following the early morning derailment at a junction in south London.
Firefighters battled to free passengers trapped when the tram derailed on a line in Croydon.
The London Ambulance Service said more than 50 people had been taken to hospital.
Witnesses said the incident, involving a two-carriage vehicle, happened on a fast bend near a tunnel.
Police confirmed they were called to the scene near Sandilands tram stop in Croydon at around 6.10am.
Officers said they were dealing with a “very serious” incident.
“Multiple resources” from the London Fire Brigade and the London Ambulance Service were on the scene. London Fire Brigade sent eight fire engines and more than 70 firefighters to the scene at Addiscombe Road.
Fire crews using specialist equipment freed a number of people but two remained inside the tram at 9.45am.
Media relations officer Hannah Collier, 23, who lives nearby, said she saw people being carried away on stretchers. She said: “I was in bed watching the election when I heard a massive crash at about 6.15am, which I thought was the wind. “Then I heard people shouting and then the emergency services arriving. Later I saw at least one person being brought out on a stretcher.
“I’d say there are roughly 20-30 emergency vehicles there now. Then they started bringing up the casualties, some very seriously injured.”
Adil Salahi, whose property overlooks the track, said the noise he heard was “sudden”.
The 76-year-old said: “It was about 6.10am to 6.15am. I thought it was something in the garage doors. Then I thought it was some lorry.”
James Long, who lives yards away from the scene, said: “It happened on a sharp bend on the approach to Sandilands tram stop. I’ve never seen so any emergency services attend a scene.”
Miguel John, who was on a bus to Bromley when it stopped by Sandilands tram stop, added: “The road hadn’t been shut off yet but emergency services were already at the scene, this would have been around 6.30am.
“By this point more emergency services were flooding to the scene and a police car shut off the road with vehicles being ushered down Elgin Road towards Addiscombe. But it was obvious it was very, very serious due to the amount of emergency services at the scene.
“At first there would have been roughly between six or 10 (vehicles) ... as time passed a lot more arrived and continued to arrive.
“Visibly from where I was about two fire engines, two to three ambulances, several police cars and then more arrived as time went on.
“I think that’s how everyone knew it was very serious, especially how quickly they acted to shut off the road.”
The tram derailed on a stretch of track around 200 yards from Sandilands tram station where emergency crews could be seen working alongside the carriage, which was lying diagonally across the tracks.
Empty stretchers could be seen laid on the side of the track.
The scene is overlooked by a small road bridge and concealed from view by trees and foliage. The Croydon Tramlink line was closed between Reeves Corner and Addiscombe village, while police set up a cordon stretching more than 400 metres along Addiscombe Road.
Mayor of London Sadiq Khan said: “I am in contact with emergency services and Transport for London, who are working extremely hard to get the situation under control and treat those who have been injured. My thoughts are with all those involved in this incident.
“We are asking people to please visit the TfL website, tfl.gov.uk, for the latest travel information.”
The Croydon Tramlink opened in 2000, becoming the first tram system in London since 1952.
The network consists of 39 stops along 17 miles of track, a mixture of street track shared with other traffic, dedicated track in public roads and off-street tram lines.
Tram accidents are extremely rare and most incidents involve collisions with other vehicles or pedestrians or cyclists being hit by trams.
Members of the emergency services work next to a tram after it overturned injuring and trapping passengers in Croydon, south London, yesterday.
