SAN FRANCISCO -- Federal investigators says they have reviewed airport surveillance video to determine whether an emergency vehicle ran over one of the victims of the plane crash at San Francisco International Airport but have not been able to reach any conclusions.

National Transportation Safety Board chairwoman Deborah Hersman on Monday called the possibility that a teenage girl was run over a "very serious issue." She said investigators want to make sure they have all the facts before reaching any conclusions.

Hersman said the coroner has not yet determined the girl's cause of death.

San Francisco Fire Chief Joanne Hayes-White and Assistant Deputy Chief Dale Carnes both said earlier Monday that one of the two teenage girls killed in the crash may have been struck by an emergency vehicle.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

One of two teenage girls killed in an Asiana jet crash at San Francisco International Airport might have been struck by an emergency vehicle responding to Saturday's crash, fire officials said on Monday.

Fire Chief Joanne Hayes-White and Assistant Deputy Chief Dale Carnes both raised the possibility at a news conference with first responders.

"There was a possibility one of two fatalities might have been contacted by one of our apparatus at one point during the incident," Carnes said.

San Mateo County Coroner Robert Foucrault earlier said his office was conducting an autopsy to determine whether one of the victims survived the crash but was run over and killed by a responding vehicle. He said his staff was notified of the possibility by senior San Francisco Fire Department officials at the crash site on Saturday.

Remarkably, 305 of 307 passengers and crew survived the crash and more than a third didn't even require hospitalization. Only a small number were critically injured.

Investigators said Asiana Airlines Flight 214 was traveling "significantly below" the target speed during its approach and that the crew tried to abort the landing just before it smashed onto the runway. What they don't yet know is whether the pilot's inexperience with the Boeing 777 and at San Francisco's airport played a role. Officials said the probe will also focus on whether the airport or plane's equipment also could have malfunctioned.

The South Korea government said officials will inspect engines and landing equipment on all Boeing 777 planes owned by Asiana and Korean Air, the national carrier.

Investigators said the weather was unusually fair for foggy San Francisco. The winds were mild, too. During the descent, with their throttles set to idle, the pilots never discussed having any problems with the plane or its positioning until it was too late.

Firefighters said they encountered smoke, leaking jet fuel and passengers coming down on chutes when they arrived. Lt. Christine Emmons said Monday at the news conference that she and her partner ran up a chute into the plane and found four passengers trapped in the back. The conditions in the plane were changing rapidly, with the fire coming down on rescuers and the smoke thickening as the trapped passengers were pulled out to safety, she said.

Seven seconds before the Boeing 777 struck down, a member of the flight crew made a call to increase the jet's lagging speed, National Transportation Safety Board chief Deborah Hersman said at a briefing based on the plane's cockpit and flight data recorders. Three seconds later came a warning that the plane was about to stall. Just 2 1/2 seconds later, the crew tried to abort the landing and go back up for another try. The air traffic controller guiding the plane heard the crash that followed almost instantly, Hersman said.