Police have arrested the driver of a tram which derailed in Croydon, south London, killing several people, the British Transport police (BTP) confirmed on Wednesday afternoon.
"At least" seven people have died, and more than 50 people have been taken to hospital for their injuries, BTP confirmed.
"This is a tragic incident and our hearts and thoughts go out to all those affected," BTP deputy chief constable Adrian Hanstock said in a statement on Wednesday evening.
“When officers arrived on scene this morning shortly after 6am, they were met with a complex and challenging situation," Hanstock continued.
“Together with our partners from the other emergency services and with support from London resilience agencies, they have worked through the day, and will continue to work throughout the night, at the scene.
“After liaison with the Coroner, we can confirm that at least seven people have lost their lives as a result of this incident."
Hanstock added that identifying those who had died would be a "complex and lengthy process," and that officers would be on the scene for at least the next 24 hours carrying out forensic examinations to provide to coroners.
"We want to ensure we get this right," he said.
Firefighters were able to release a number of people from the tram during the early hours of this morning, but two remain trapped inside, the London Fire Brigade said.
Heard a massive crash outside my window, now emergency services everywhere for the overturned tram, hope everyone i… https://t.co/IXfWGypRuY
Emergency services were called at 6.13am to an incident at Addiscombe Road, close to the Sandilands tram stop. Pedestrians nearby said they heard a "massive crash" during the early hours of the morning.
Police officers in Croydon described the situation as a "serious incident" and instructed people to avoid the area.
🚧 SANDILANDS 🚧 Emergency Services are dealing with a serious incident at #Sandilands tram stop. Please avoid the ar… https://t.co/wlXmJwxKgX
In a statement a spokesperson for the London Ambulance Service (LAS) said that that a number of patients have been treated and more than 50 have been taken to hospital. The LAS also told people to "please only call in an emergency" as they were busy with the tram incident.
In a Facebook post, London mayor Sadiq Khan said he was in contact with emergency services and Transport for London (TfL), 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," he added.
My statement following this morning's incident at Sandilands tram stop in Croydon: https://t.co/FPpgUItI2H