Seven people have been killed and 50 injured, after a tram overturned in Croydon this morning, Police have said.
Emergency services were called at 6.13am when the tram came off the tracks near the Sandiland stop.
More than 70 firefighters, and London Ambulance staff attended the scene, while London's Air Ambulance sent five doctors and four paramedics in rapid response cars.
In a statement, British Transport Police Deputy Chief Constable Adrian Hanstock said: “This is a tragic incident and our hearts and thoughts go out to all those affected.
“When officers arrived on scene this morning shortly after 6am, they were met with a complex and challenging situation.
“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.
“Our officers will continue to work tirelessly throughout the evening to formally identify them and provide care and support for their families.
“Identifying those who have died can be a complex and lengthy process and we want to ensure we get this right.
“We expect to be at the scene for at least the next 24 hours, continuing searches and carrying out forensic examinations in support of the investigation into the circumstances, and in order to provide a report for the Coroner.
“Tomorrow, we will assess how and when it is appropriate to recover the tram and remove it from the tracks.
“I want to thank everyone who assisted at the scene, and behind the scenes, in Croydon today.
“In the coming days, we will continue to work alongside the Rail Accident Investigation Branch to establish the circumstances of how this happened.
“At this stage it is too early to speculate on a single factor being the cause of this incident.”
A 42-year-old man from Beckenham has been arrested on suspicion of manslaughter and is currently in police custody.
Hannah Collier, who lives nearby told the Standard: “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."
Peter McKenna, deputy director of operations at London Ambulance Service said: "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 and took 51 patients to hospital. 20 were taken to St George's University Hospital and 31 to Croydon University Hospital."
A statement from St George's Hospital said: "Following an overturned tram incident in Croydon early this morning, 20 people have been brought to St George’s Hospital in Tooting for treatment.
"Of these 20 patients, four are seriously injured. All patients are being cared for by our clinical teams."
The Rail Accident Investigation Bureau is on the scene and looking into the incident, British Transport Police say.
The Mayor of London Sadiq Khan said his thoughts are with those involved.
TfL Commissioner Mike Brown said: "I am devastated for the families and friends of those who have lost their lives and those who have been injured.
"Clearly something has gone catastrophically wrong and we will work tirelessly and quickly with the emergency services, the tram operator FirstGroup and others to establish the cause. My team will continue to be available in Croydon to assist those affected and the wider community in the area. "
This is the first fatal rail crash in London since the Ladbroke Grove accident in 1999.
BTP said anyone concerned about friends or relatives who may have been involved in the incident can call the Casualty Bureau on the following number: 0800 056 0154.