A US coroner is working to determine whether one of the victims of the San Francisco plane crash was run over and killed by an emergency vehicle.

Two Chinese teenagers - Ye Mengyuan, 16, and Wang Linjia, 17 - were killed after the Asiana Airlines Boeing 777

More than 30 people remain in hospital, with injuries including paralysis, fractures and internal bleeding.

San Francisco fire chief Joanne Hayes-White says one of the girls may have been run over by an airport fire engine rushing to the scene.

"As you can imagine it was a very dynamic environment dealing with an active aircraft fire and trying to rescue somewhere in the realm of 300 victims," she told the San Francisco Chronicle.

"Based on the injuries sustained, it could have been one of our vehicles that added to the injuries, or another vehicle."

The head of the airport's fire team, Dale Carnes, says his squad is assisting officials investigating the incident.

"We are also conducting an internal investigation of our own trying to clearly establish the facts of what happened," he said.

It is not known which girl may have been hit by the vehicle.

Officials say the other girl appeared to have died from injuries suffered as she was hurled out of the plane when its tail broke off in the crash.

The two best friends were coming to visit Stanford University, just south of San Francisco, and to attend a summer camp at a local Christian school, the Chronicle reported.

Transport safety officials say the plane was travelling well below the recommended speed as it attempted to land.

The flight data recorder shows that as the Boeing 777 approached the runway its pilots were warned four seconds before the crash that the aircraft was likely to stall and asked to abort the landing.

The request to abort was captured on the cockpit voice recorder 1.5 seconds before the plane crashed.

Asiana has , but the for the crash.

He had earlier said the plane had no known mechanical problems.

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.