The Rail Accident Investigation Branch said the tram derailed as it was negotiating a "sharp, left-hand curve" with a speed limit of 12 mph.

 A spokesman said: "Initial indications suggest that the tram was travelling at a significantly higher speed than is permitted."

Dr Phil Moss, the clinical director of the emergency department at St George's Hospital in Tooting, south east London, said three people are having surgery at the hospital. 

He would not give any detail about the ages or injuries of any of the 20 patients who they treated from the tram incident. 

Dr Moss said: "This was a very serious incident and the injuries sustained were very serious. We know there have been some fatalities at the scene today. 

"The patients who have gone to the operating theatre will certainly be kept overnight if not for several days or even weeks."

 Emergency medical teams at the hospital dealt with four "majorly injured" patients and 16 walking wounded, he said.

"Three of those patients are now in the operating theatre and one of the patients who was thought to be seriously injured patients has now fortunately been discharged. The remaining 16 patients are in the process of being discharged. 

A tram which derailed in south London killing at least five people was travelling at a "significantly higher speed than is permitted", the Rail Accident Investigation Branch said.

Croydon Central MP Gavin Barwell says trams are usually very safe: "It's one of the best things about our borough, we've got this incredible, environmentally friendly public transport system that gets people into the town centre very quickly. 

"Thousands of my constituents use the service every day so lots of people will be sitting there today thinking it could have been me on that tram today. So what we need is a thorough investigation that explains why the accident happened and some reassurance."

Image source, PA

After the sirens stopped there is now an eerie silence on the road where the tram tipped over. 

Instead of the usual flow of cars, buses and trams, there are just a few people standing by the police cordon looking at the wreckage. 

As I passed one tram stop on the way and briefly stopped to look at the matrix sign, a man said "there aren't any trams today," clearly shaken by what had happened. 

The cordon is at least 200 metres from the accident site but we can see police officers and firefighters still examining the tram. 

The recovery stage has now begun - as well as the investigation into a how a normal, midweek morning commute ended so disastrously.

Mayor of London Sadiq Khan said that the number of dead in the Croydon tram crash "may well increase" above the five already confirmed by police.

It 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.

David Friend
BBC Radio London

Listen to Drivetime, from 16:00 with Chris Rogers, for extensive coverage of the Croydon tram crash. 

Reporter Anna O’Neill is at the scene and we’ll bring you reaction throughout the evening. 

We’ll also be gauging London’s response to the news that Donald Trump is to become the 45th President of the United States. Let us know what you think by calling 0207 224 2000.

Image source, PA

Peter McKenna, Deputy Director of Operations at London Ambulance Service said:

“We would like to express our sincere condolences to everyone affected by this tragic incident, and thank our ambulance staff for their work under very difficult circumstances today.

“We were called at 606:13 to reports of a tram derailment at Addiscombe Road in Croydon.

“We sent 22 ambulance crews, 12 officers, and two advanced paramedic practitioners to the scene, alongside our hazardous area response team, who are trained to provide emergency medical care in hazardous areas such as confined spaces or where there may be hazardous materials.

“Two trauma teams from London’s Air Ambulance and a command support vehicle were also dispatched.

“We have treated a number of patients at the scene, mainly for minor injuries such as cuts and bruises, however very sadly some people have died and others have suffered serious injuries.

"We took 51 patients to hospital, 20 of whom were taken to St George’s University Hospital and 31 to Croydon University Hospital.

“We remain on scene, supporting our emergency service colleagues as they deal with this incident.

Five people have died and dozens more have been injured after a tram overturned in south London, police have said.  

BBC Radio 5 live

Image source, Peter Allan Jones

Peter Allan Jones lives in a flat opposite where the tram derailed this morning.

He told BBC Radio 5 live what he saw and heard: "It's only after we heard the sort of shouting and screaming and the flashing lights outside, that we sort of sat up and took notice of what was going on. 

"They were coming down the tracks from where the accident happened towards the main road, some looked like walking injured, some of them a few head bandages around their heads. 

"One guy - I'm not sure what he was shouting about but I think he had somebody who was still in there, might be trapped. He wanted to go back and the police were restraining him and telling him to come with them. 

"Everyone else seemed quite sombre and quite shocked. It was a weird eerie silence even with the sirens in the background."

Image source, Getty Images

• Five people have died
• 51 people are being treated in two London hospitals
• Four people have been seriously injured
• Emergency services are working to free two people still trapped in the two-vehicle carriage
• The tram's driver has been arrested
• The tram remains overturned near to Sandilands tram stop

Finn Brennan, of the train drivers' union Aslef, said the incident was "truly dreadful". 

He said: "Lives have been lost and there are many serious injuries. This is a tragedy for all those involved. For the women and men who set out this morning on their journey to work and suffered this awful accident and their families, the grief and pain must be terrible. 

"There will be a full investigation into the causes of this incident by the RAIB (Rail Accident Investigation Branch) and others. 

There should be no rush to judgment or to place blame until the facts are known.

"For now, our thoughts are with all those injured and lost, their families, Tramlink staff and the emergency service and NHS staff working to save lives as they do every day."