At least seven people were killed and more than 50 injured when a tram overturned on Wednesday morning in south London, police said and later confirmed the driver had been arrested, Reuters reports.

Early indications were that the tram was travelling too fast on a sharp bend, investigators said.

Emergency services were called at about 6:10 am (0610 GMT) to reports that the two-carriage tram had derailed near a stop close to central Croydon, a large suburb to the south of the British capital and a major transport hub.

"We can confirm a total of at least seven people have sadly died at Croydon," police said in a statement. "Officers continue to work at the scene.

A police spokesman later said the tram`s driver had been arrested, but did not specify why.

The independent Rail Accident Investigation Branch said the derailment had happened on a sharp curve with a 12 mph (20 kph) speed limit.

"Initial indications suggest that the tram was travelling at a significantly higher speed than is permitted," it said in a statement.

A London Ambulance spokesman said 51 others had been taken to hospital, some with serious injuries. Eight fire engines, five specialist rescue units and more than 70 firefighters attended the scene using heavy cutting equipment to free those trapped.

Television pictures showed the tram lying on its side across the tracks not far from the Sandilands stop near a junction where the line divides. Police said investigations were ongoing into the cause of the accident which took place in heavy rain.

Local resident Hannah Collier, 23, told local media she had seen very seriously injured casualties being taken away on stretchers.

"I was in bed watching the election when I heard a massive crash at about 6:15 am, which I thought was the wind," she said. "Then I heard people shouting and then the emergency services arriving."

Prime Minister Theresa May said her thoughts and prayers were with those affected by "this terrible incident".

Wednesday`s incident was the greatest loss of life in a British rail accident since seven people were killed and 70 injured when a high-speed train from London came off the tracks at Potters Bar station north of the capital in 2002.

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17:04

Emergency workers were still at the scene of the derailment in Croydon, trying to free two people trapped in the wreckage of the two-carriage train that tipped on its side next to an underpass. The cause of the derailment was under investigation.

"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.

London`s fire department said eight fire engines and four specialist rescue units were at the scene. 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. People were carried away on stretchers."

Another neighbor, 76-year-old Adil Salahi, whose property overlooks the track, said he was praying when he heard the sudden noise.

"I could not move and try to check what it is," he said. "I thought it was something in the garage doors. Then I thought it was some lorry."

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

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