Media playback is unsupported on your device Media caption Passenger Ben Levy: "It happened in a flash, nobody was worried about anything"

A Boeing 777 aircraft has crash-landed at San Francisco international airport, killing two people and injuring dozens more, officials say.

More than 300 people were on Asiana Airlines Flight 214, from South Korea's capital, Seoul. Passengers and crew escaped down emergency slides as the plane burst into flames.

Asiana has confirmed two female Chinese teenagers have died in the crash.

The airline said mechanical problems did not cause the crash.

The two Chinese teenagers who died had been seated at the back of the aircraft, said Asiana, South Korea's second largest carrier.

They are believed to be the first-ever fatalities in a Boeing 777 crash.

"Currently we understand that there were no engine or mechanical problems," Asiana chief executive Yoon Young-Doo told a news conference in Seoul.

Media playback is unsupported on your device Media caption Eyewitness Ki Siadatan: "[The plane] seemed like it was out of control"

Boeing said in a statement it would provide technical assistance to the investigation.

Early indications suggest the plane came in too short and hit the seawall at the airport.

Eight adults and two children who suffered critical injuries are being treated at San Francisco General Hospital, hospital spokesperson Rachael Kagan said.

Altogether 181 people were taken to hospital, mostly with minor injuries.

Image caption Smoke billows from the burning plane after it crash-landed on San Francisco International Airport's Runway 28L Image caption More than 300 people were on Asiana Airlines Flight 214, which had taken off from South Korea's capital, Seoul Image caption Firefighters and rescue teams are at the scene Image caption The two Chinese teenagers who died had been seated at the back of the aircraft Image caption The tail fin broke off during the crash and could be seen lying on its side apart from the main wreckage Image caption Fire engines could be seen spraying a white fire retardant into gaping holes in the wrecked plane's roof previous slide next slide

There were 291 passengers and 16 crew on board, Asiana said.

Nationalities on board included 141 Chinese, 77 South Koreans and 61 US citizens, the airline said.

Rescue teams initially took 49 people deemed to be in a serious condition to nearby hospitals, officials said.

Boeing 777 fact sheet Twin-engine jet launched in June 1995

One of the world's most popular long-distance planes

Seats between 300 and 380 passengers

Has flown around five million flights

Often used for nonstop flights of 16 hours or more

Prior to Asiana crash, only one fatal accident when a crew member died during a re-fuelling fire at Denver International Airport in September 2001

Some 190 people walked to safety from the plane, many of whom were later treated for minor injuries.

All of the passengers have now been accounted for.

While the sequence of events remains unclear, it appeared the plane landed and then crashed on San Francisco International Airport's Runway 28L, said Federal Aviation Administration spokeswoman Laura Brown.

Footage of the scene showed debris strewn on the runway and smoke pouring from the jet, as fire crews sprayed a white fire retardant into gaping holes in the craft's roof.

One engine and the tail fin appeared to have broken away from the main wreckage.

'Out of control'

Passenger Ben Levy said there had been no warning of problems before the crash. "It happened in a flash, nobody was worried about anything," he said.

But once the aircraft crashed, "there was chaos, disbelief, screaming".

"My seat had been pushed to the floor, it was a mess everywhere," Mr Levy recalled.

Nevertheless, people "calmed down pretty quickly" and evacuated the plane without pushing or stepping on each other.

Meanwhile another passenger, David Eun, tweeted a picture of people evacuating down the plane's emergency inflatable slides and wrote: "I just crash landed at SFO. Tail ripped off. Most everyone seems fine. I'm ok. Surreal..."

Media playback is unsupported on your device Media caption City Mayor Ed Lee: "This is still a fluid and active scene"

Mr Eun, who describes himself as a "digital media guy" and "frequent flier", added: "Fire and rescue people all over the place. They're evacuating the injured. Haven't felt this way since 9/11."

A witness to the crash, Ki Siadatan, said the plane "looked out of control" as it descended over San Francisco Bay to land just before 11:30 (18:30 GMT).

"We heard a 'boom' and saw the plane disappear into a cloud of dust and smoke," he told the BBC. "There was then a second explosion."

He saw events unfold from the balcony of his home in the Millbrae area of San Francisco, which overlooks the airport.

Weather conditions were fine and there was little wind, he added.

Arrivals and departures at the airport have been suspended since the incident.

The twin-engine Boeing 777 has a good safety record as a long-haul aircraft and is used by many major carriers.