At least two people were killed and several others were injured as a helicopter crashed into a crane at a building site in central London on Wednesday morning, officials said.
The London Fire Brigade said the fire has been brought under control.
A huge flume of grey smoke billowed out of the crash site where the helicopter plummeted at around 8 am after hitting a crane sending out a huge fireball.
According to reports, the helicopter wreckage landed on two cars.
"Eight fire engines and four fire rescue units and around 60 firefighters plus officers are attending a helicopter crash near Wandsworth Road in South Lambeth. Firefighters have brought the fire under control," London Fire Brigade website said.
"The police have confirmed that two people have died at the scene. Firefighters have rescued a man from a burning car. Two people have been taken to hospital by London Ambulance Service crews," it said.
"Firefighters are also attending reports of a crane in a precarious position Saint Georges Whalf, SW8. Four fire engines and two fire rescue units are in attendance," it said.
The London Fire Brigade said it was called at 8:00 am.
London Ambulance Service said in a statement: "We have treated four patients for minor injuries, and two of them were taken to St Thomas' Hospital and two - a man and a woman - were taken to King's College Hospital."
"We are treating four patients on scene for shock," it said.
Train services at Vauxhall and Waterloo stations have been suspended after the mishap.
The Metropolitan Police said there was no suggestion to a terrorism link to the incident at the moment.
Met Police have told BBC News: "It´s very early stages but there is no suggestion yet this was terrorism. There is no SO (Special Operations) involvement at the moment."
Ex-BBC producer Paul Ferguson told the news channel that the helicopter "plummeted straight into the ground".
"The building the helicopter hit is shrouded in mist," he said.
Erin Rogers, who was waiting at a bus stop outside Vauxhall station, told BBC: "It was a bit surreal actually. I just had a coffee in my hand, I looked up, heard a bang and saw bits of crane debris falling to the floor. Then the helicopter was in flames. The rest of the people at the bus station were looking on going ´What was that?´."
"It´s something I will never forget for a long time," Rogers said.
One Aaron James Rodgers tweeted: "Just witness an horrific crash! Helicopter hit a crane, spiralled into the ground!"
Another Adam Smith posted: "Sirens and traffic everywhere! Hope nobody got hurt in this helicopter crash."
One Manda McCann said: "This helicopter crash looks pretty bad!! Hope ther isn´t people under it all !"