Fire trucks surrounded the Boeing 777, which had taken off from Beijing, after it landed early in the afternoon, spraying fire retardant foam around the aircraft.
The plane's wheels appeared to collapse as it came down in the grass in front of the airport's southern runway, witness John Rowland told the British Broadcasting Corp.
"It crashed into the runway, debris was flying everywhere, there was an enormous bang and it skidded sideways," he said.
London Ambulance Service said eight people had been taken to a hospital with minor injuries.
CBS News reported that passengers were treated for cuts and bruises.
The accident at one of Heathrow's two runways occurred just before a plane carrying British Prime Minister Gordon Brown and a delegation of business leaders, including Virgin Chairman Richard Branson, was about to depart for China. The prime minister's plane was about half a mile away.
The crash forced Europe's busiest airport to temporarily halt departures and arrivals while emergency crews worked at the scene. Planes were still taking off and landing on Heathrow's northern runway, air traffic control company Nats said. Some other flights were diverted to other airports, Heathrow said on its Web site.
The Air Accident Investigation Branch was investigating, British Airways Chief Executive Willie Walsh told reporters, adding the airline didn't want to speculate on the cause.
The passengers had been taken to a center, where airline staff were looking after them, Walsh said.
"The customers on board the aircraft are generally in good spirits, I know they are anxious to get back to their friends," Walsh said. "They are being interviewed by the police until all the relevant details have been taken."
It was the first accident involving the Boeing 777 since the plane entered service in 1995, said Boeing spokeswoman Liz Verdier in Seattle.
The Boeing 777, one of 42 in the BA fleet, was relatively new at 6-years-old, Walsh said.
"The captain of the aircraft is one of our most experienced and has been flying with us for nearly 20 years," he said.
Emergency workers surrounded the plane and firefighters sprayed fire retardant foam as a precaution as the 16-member crew evacuated passengers on inflatable chutes.
Passenger Jerome Ensinck told the BBC that he at first thought the plane had made a hard landing.
"There was no indication that we were going to have a bad landing," he said. "When we hit the ground it was extremely rough."
"Then the emergency exits were opened and we were all told we should go through as quickly as possible, and the moment I was away from the plane I started to realize that the undercarriage was away, and we had missed the runway, Ensinck said.
"Now I realize I've had a close call," he said.
Robert Cullemore of Aviation Economics, a London-based aviation consultancy, said a pilot from a competing airline told him officials believed the cause of the accident was wind shear, a sudden gust of wind.
"It can happen anytime anywhere and if it happens you just hope there is no airplane nearby," Cullemore said.
He said the pilot kept the plane in the air long enough to prevent a disastrous outcome.
"If it had landed 200 meters shorter than it did, it may have hit perimeter fence and obviously some other buildings and the car park, clearly we would be dealing with fatalities and obvious damage," Cullemore said.
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