An international passenger plane has crash landed short of the runway at Heathrow Airport.
All 136 passengers and 16 crew escaped down the Boeing 777's emergency chutes after British Airways flight BA038 from Beijing came down.
Six people have been taken to hospital suffering minor injuries, reports say.
The incident happened as Prime Minister Gordon Brown was due to leave Heathrow for China and India. His flight was delayed because of the incident.
Downing Street said at about 1430 GMT that Gordon Brown had taken off. On its approach it took the runway too low, just missing the roof of my cab
John Rowland, eyewitness
Eyewitness accounts
The south runway is closed while investigators examine the scene - the north runway remains open.
Eyewitness John Rowland said: "The plane's wheels collapsed, doors were flown open.
"On its approach it took the runway too low, just missing the roof of my cab.
"It crashed into the runway, debris was flying everywhere, there was an enormous bang and it skidded sideways."
BA has set up a helpline for anyone concerned about friends or relatives: 0800 3894193
BA said the cabin crew had done an "excellent job" evacuating passengers, and that it would release more information as soon as it was available.
A telephone helpline has been set up for anyone concerned about friends or relatives on 0800 3894193.
Chief executive of BA Willie Walsh said he was "very proud" of the crew.
Fernando Pardo was a passenger on the plane itself. He told the BBC there was "no sign whatsoever of any trouble until we touched the ground".
"It was so quick that you could not even realise what exactly happened. There was no panic at all," Mr Pardo said.
Huge amount of smoke
Another eyewitness, Nick Gray, told BBC News: "We were taxiing along ready to take off and certainly out of the window I could see a plane coming in to land.
"I'm not quite sure if the undercarriage was missing or not, but certainly what we saw was the plane coming down.