An international passenger plane has crash landed short of the south runway at Heathrow Airport.
All 136 passengers and 16 crew escaped down the emergency chutes after British Airways flight BA038 from Beijing lost its rear undercarriage and came down.
Six people have been taken to hospital suffering minor injuries, reports say.
Passengers at Heathrow airport are suffering travel disruption, with all British Airways short haul flights from the airport cancelled.
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.
The south runway is closed while investigators examine the scene – the north runway remains open.
All short haul flights from Terminal 4 have been cancelled.
Police have said the incident involving the Boeing 777 was not terror-related.
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 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.
A London Ambulance spokeswoman said there were eight ambulances at Heathrow and six passengers had been taken to nearby Hillingdon Hospital with minor injuries.
She could not give details of the type of injuries the passengers suffered.
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.
“There were some sparks as the undercarriage or the bottom of the plane actually touched the runway – certainly a huge amount of smoke coming up from that.
“It was incredibly efficient the speed that people got off the aircraft.
“There seems to have been regular dousing of foam on the port engine which obviously probably was the hottest one where the plane landed.
“Certainly there is a lot of activity and lots of vehicles with flashing lights all around the plane.”
Some flights bound for Heathrow are being diverted to Stansted and Luton Airports.
Manchester Airport said its BA flights to Heathrow on Thursday afternoon had been cancelled.
John McDonnell MP, whose Hayes and Harlington constituency includes Heathrow, told the BBC that the incident underlined concerns about extending the airport.
“This is a near miracle that neither passengers or anyone on the ground has been seriously injured,” Mr McDonnell said.