Steve Parsons, AP
Emergency service workers attend the scene of a derailed tram in Croydon, south London, Wednesday Nov. 9, 2016. A tram derailed in London before dawn on Wednesday, leaving at least 50 people injured and several trapped, the emergency services said.

LONDON — A tram derailed in south London before dawn on Wednesday, resulting in "some loss of life" and injuring more than 50 people, police and emergency services said.

Emergency workers were still at the scene of the derailment in Croydon more than six hours later, trying to free two people trapped in the wreckage of the two-carriage train that tipped on its side next to an underpass.

British Transport Police said they had arrested a man — reportedly the tram's driver — and rail accident investigators were probing the cause of the derailment.

"A number of people have been taken to hospital with injuries and sadly it looks as though there has been some loss of life," Assistant Chief Constable Robin Smith told reporters. He said it was too early to confirm the number of dead.

London's fire department said eight fire engines and four specialist rescue units were at the scene. The rescue units, which are used in complex incidents, are equipped with heavy lifting and cutting tools, together with longer duration breathing apparatus and floodlighting.

Emergency services called to the Sandilands tram stop at around 6:10 a.m. (0610 GMT, 1:10 a.m. EST).

"I heard a massive crash at about 6.15 a.m., then heard shouting, then the emergency services arrived," said Hannah Collier, 23, a resident. "They started bringing up the casualties, some very seriously injured."

Station manager Joe Kenny said "firefighters have released a number of people and two people remain trapped."

The London Ambulance Service said it treated a number of people at the scene, and more than 50 had been hospitalized.

The British capital's only tram network operates in the southern end of the city, serving 27 million passengers in the last year.