SERIOUS INTERIOR DAMAGE

People on the flight said nothing seemed amiss until moments before the crash. Pictures taken by survivors showed passengers hurrying out of the wrecked plane, some on evacuation slides. Thick smoke billowed from the fuselage and TV footage showed the aircraft gutted by fire. Much of its roof was gone.

Interior damage to the plane also was extreme, Hersman said on CNN earlier on Sunday.

"You can see the devastation from the outside of the aircraft, the burn-through, the damage to the external fuselage," she said. "But what you can't see is the damage internally. That is really striking."

The NTSB released photos showing the wrecked interior cabin with oxygen masks dangling from the ceiling.

Hersman said the first emergency workers to arrive at the scene included 23 people in nine vehicles. San Francisco Mayor Ed Lee said a total of 225 first responders were involved.

"As chaotic as the site was yesterday, I think a number of miracles occurred to save many more lives," Lee said at the airport news conference. Appearing later at San Francisco General Hospital, he declined to address whether one of the Chinese teenagers may have been run over.

It was the first fatal commercial airline accident in the United States since a regional plane operated by Colgan Air crashed in New York in 2009.

Asiana, South Korea's junior carrier, has had two other fatal crashes in its 25-year history.