Asiana Airlines says the pilot in charge of landing a plane that crashed short of the runway at San Francisco airport was in training for the long-range jet.

The Boeing 777 was en route from Seoul when it crash landed and burst into flames at the weekend, killing two Chinese teenagers.

Passengers managed to evacuate the plane via emergency slides before the fire took hold but local authorities say more than 180 people were injured, at least two dozen of them seriously.

A spokeswoman for Asiana said it was pilot Lee Kang-kook's first flight to the airport with the jet.

"He was in training. Even a veteran gets training (for a new jet)," she said.

Key points: Asiana plane crashed short of the runway at San Francisco Airport

Asiana plane crashed short of the runway at San Francisco Airport The airline says the pilot was in training to fly the Boeing 777 jet

The airline says the pilot was in training to fly the Boeing 777 jet Two Chinese teenagers were killed and more than 180 passengers injured

Two Chinese teenagers were killed and more than 180 passengers injured The most severely injured suffered paralysis, fractures, head trauma and internal bleeding

The most severely injured suffered paralysis, fractures, head trauma and internal bleeding Two people had road rash, suggesting they were dragged

Two people had road rash, suggesting they were dragged Investigators are hunting for clues as to what caused the plane to crash

Investigators are hunting for clues as to what caused the plane to crash The pilots will be interviewed in the coming days

"He has a lot of experience and has previously flown to San Francisco on different planes including the B747... and he was assisted by another pilot who has more experience with the 777."

She said the pilot, who started his career at Asiana as an intern in 1994, had 9,793 hours of flying experience, but only 43 hours with the Boeing 777 jet.

The US National Transportation Safety Board said the plane was travelling "significantly below" its intended speed and its crew tried to abort the landing just seconds before it hit the seawall in front of the runway.

Officials say it is too early to determine whether pilot error or mechanical failure are to blame for the crash. The control tower was not alerted to any plane issues.

The pilots are due to be interviewed in the coming days.

Doctor reveals survivors' severe injuries

Meanwhile, a doctor has revealed the extent of injuries suffered by passengers on board the plane.

Margaret Knudson, interim surgery chief at the San Francisco General Hospital, says the most severely injured are paralysed, unconscious or dealing with serious abdominal bleeding.

"[Doctors saw] large amounts of abdominal injuries, a huge amount of spine fracture, some of which include paralysis, and head trauma and multiple type of orthopaedic injuries," she said.

"[Two patients] had severe road rash, suggesting they were dragged. Not sure if those patients were outside of the plane and this is what happened to them but both of those patients are alive."

The black boxes from the Asiana plane ( Twitter: @NTSB )

She says all of the patients who are able to speak told doctors they had been sitting in the back of the jet, where the tail broke off as the plane smashed into the end of the runway.

But she says 15 or 16 patients have not yet regained consciousness.

"Some of our patients have been operated on twice already, and there's going to be many many more surgeries to come still," she said.

Flight 214 originated in Shanghai, and had 307 people on board - 291 passengers and 16 crew.

Witnesses reported seeing a fireball and said the aircraft spun around before coming to rest on its belly at the end of the runway.

The crash sheared off the plane's landing gear and tore the tail off the fuselage. Large portions of the plane's body were burned out in the fire that then erupted.

The head of the Asiana airline, Yoon Young-doo, says the Boeing 777 jet did not have mechanical problems when it crashed.

"For now, we acknowledge that there were no problems caused by the 777-200 plane or [its] engines," he said.

Mr Yoon has declined to comment directly on whether the crash was due to pilot error.

Sorry, this video has expired Crash evidence points to pilot error: safety expert ( Virginia Trioli )

San Francisco's fire chief Joanne Hayes-White says the airline crew on board showed great heroism and professionalism.

"My understanding is the crew of Asiana airlines did a phenomenal job in making sure that passengers first and they stayed on to make sure that everyone was brought to safety," she said.

"I interacted with one of the crew managers, and she was actually so composed I actually thought that she was brought in from the terminal and she actually had evacuated herself off the plane."

Most of the passengers were from China, Korea and the US. Asiana says the two teenage girls who died had been seated at the back of the aircraft.

The Boeing 777, a family of twin-engined long-haul aircraft, is rated as one of the safest aircraft in the world and has been since it started flying in 1995.

There are more than 1,100 in service, with a rate of one accident for every 18 million hours of flying time. This is the first fatal accident involving the aircraft.

The Asiana Airlines Boeing 777 after it crashed while landing at San Francisco International Airport in California. ( Reuters: Jed Jacobsohn )

ABC/Reuters