At least two people were killed and 130 injured Saturday when an Asiana Airlines Boeing 777 jet crashed and caught fire as it landed short of the runway at San Francisco International Airport.

Another 60 people were still unaccounted for, the city's fire chief Joanne Hayes-White told reporters. It was not immediately clear if those people were presumed dead or had left the scene without alerting officials.

The Federal Bureau of Investigation (FBI) said there was no indication terrorism was to blame for the crash of Flight 214, which had 291 passengers and 16 crew on board when it left Seoul.

Investigators said they could not yet offer an explanation for the crash, but images appeared to suggest the aircraft struck a rocky area at the water's edge short of the runway.

Pictures showed the tail detached from the fuselage and the landing gear had also sheared off.

"At this time there are two fatalities associated with this incident," Hayes-White said.

Survivor Elliott Stone told CNN that as the plane came in to land, it appeared the pilot "sped up, like the pilot knew he was short."

"And then the back end just hit and flies up in the air and everybody's head goes up to the ceiling."

Video footage showed the jet on its belly surrounded by firefighters with debris scattered on the runway and in the surrounding area.

"It looked normal at first... the wheels were down," an unidentified man who witnessed the crash told CNN. "It just hit (the seawall) like that and the whole thing just collapsed immediately.

"It just pancaked immediately. The wings caught on the tarmac."

A National Transportation Safety Board team was heading to San Francisco to investigate the crash landing.

"Everything is on the table at this point," NTSB chairwoman Debbie Hersman told reporters in the US capital when asked if pilot error was to blame. "We have to gather the facts before we reach any conclusions."

At least 10 people, including two children, were in critical condition at San Francisco General Hospital.

One dramatic photo tweeted by a survivor showed people streaming out of the jet following the crash-landing. An inflatable slide was at the front entrance. Other emergency exits also appeared to have been used.

"I just crash landed at SFO. Tail ripped off. Most everyone seems fine. I'm ok," the passenger, David Eun, wrote on Twitter.

But another photo from above showed a more distressing scene, with most of the roof of the plane missing and the cabin seating area charred by fire. The aircraft's wings were still attached.

"I saw some passengers bleeding and being loaded onto an ambulance," another passenger, Chun Ki-Wan, told YTN TV in Seoul.

"Everything seemed to be normal before it crash-landed."

Stone said he feared for the flight crew seated in the back of the plane.

"They were sitting in the back end and got hammered because we landed short. And then they all fell out and it was just the most terrible thing I've seen," he said.

The airport was closed immediately after the incident but two runways later reopened. Some flights were diverted to Los Angeles.

Among those on board were 77 Koreans, 141 Chinese, 61 US citizens, and one Japanese national, Asiana said in a statement.

San Francisco General Hospital said it was treating six female and four male victims, including two children, all of whom were in critical condition. The adult casualties were aged between 20 and 40.

Local media cited multiple witnesses who said the plane had approached the runway at an awkward angle, with several onlookers saying they then heard a loud bang.

"You heard a pop and you immediately saw a large, brief fireball that came from underneath the aircraft," Anthony Castorani, who saw the crash from a nearby hotel, told CNN.

The accident site was covered in white foam used by firefighters, with at least six fire trucks at the scene.

The White House said President Barack Obama had been briefed on the incident, noting: "His thoughts and prayers go out to the families who lost a loved one and all those affected by the crash."

California highway police temporarily closed all roads near the facility -- a major international hub, especially for flights to and from Asia.

Asiana Airlines is based in Seoul. The twin-engine 777 aircraft is one of the world's most popular long-distance planes, often used for flights of 12 hours or more, from one continent to another.