View of the British Airways Boeing 777 after its crash-landing at Heathrow. The incident, which left 18 people injured, caused delays at the world's busiest international airport. [Photo: AFP]

A British Airways jet crash landed short of the runway at London Heathrow on Thursday, injuring 18 people and causing delays and cancellations at the world's busiest international airport.

The undercarriage of the Boeing 777 was wrecked with the back end and the engines touching the ground. Passengers poured out of emergency slides while firefighters sprayed safety foam around the jet. One passenger said he felt he had won the "lottery" by escaping unharmed.

Television pictures showed skidmarks carving up the grass ahead of the runway used by Flight BA38 from Beijing with 136 passengers and 16 crew on board. All the injuries were reported as minor.

The Air Accidents Investigation Branch (AAIB) said an initial report on the crash would be available within 48 hours, but Chief Inspector of Air Accidents David King warned that it could take more than a month for the full report to be produced.

All those on board the plane will be questioned by the AAIB, and the airliner's "black box" and cockpit voice recorders will also be checked.

Paul Venter, a passenger on the flight, said the plane hit problems just as it was about to land.

"I could hear the undercarriage come out and the next moment the plane just dropped," he said.

"The wheels came out and went for touchdown, and the next moment we just dropped. I couldn't tell you how far.

"When everything came to a standstill, I looked out of the window and the undercarriage was gone and the plane was on its belly.

"I didn't speak to the pilot, but I saw him, and he looked very pale."

Another passenger, Fernando Prado, told BBC television by telephone that all the passengers had been evacuated within two or three minutes, adding of his escape: "I won the lottery today."

BBC television quoted the pilot -- 43-year-old Peter Burkill -- as saying he had lost all power as it was landing and had to glide it in. A Heathrow spokesman said the emergency landing had happened at 12:42 pm (1242 GMT), and the plane was fully evacuated.

The incident happened shortly before Prime Minister Gordon Brown was due to take off from Heathrow for China on an official visit. His flight was briefly held up.

Brown was travelling with a party of around 30 journalists, businessmen and personalities, including Virgin chief Richard Branson and Olympic athlete Kelly Holmes.

More than 200 flights, most of which were short-haul, had to be cancelled, while a further 24 were diverted to London's other airports, as the southern runway at Heathrow was closed.

BA chief executive Willie Walsh said: "We are very proud of the way our crew safely evacuated all 136 passengers on board.

"The crew are very experienced and are trained to deal with circumstances like this."

He said the airline would cooperate fully with the AAIB's investigation.

"It would be inappropriate for me to speculate as to the likely cause of this incident," Walsh added.

According to Walsh, the aircraft in question was about six years old, and BA has 43 Boeing 777s in operation.

The nearby Hillingdon hospital reported 13 casualties, one of which would be kept overnight.

A London police spokesman said there was no suggestion that terrorism was involved.