Two people have been killed and more than 150 others injured when a plane crash landed at San Francisco International Airport, according to the city fire department.
The Asiana Airlines flight, coming from Seoul, South Korea, was believed to be carrying 291 passengers and 16 crew members.
The San Francisco Fire Department, said 181 people have been taken to various hospitals – 49 of whom are in a serious condition.
Terrorism had been ruled out as a cause of the accident, the FBI confirmed.
Eyewitnesses reported seeing the plane’s tail section break off during the crash. South Korea’s transportation ministry said the tail of the plane hit the runway before it crashed.
A fire started when the plane landed and passengers were forced to use emergency inflatable slides to escape the aircraft, witnesses added.
Parts of the plane’s tail and the landing gear were strewn across the runway. TV footage showed the top of the fuselage had been burned away and one engine appeared to have broken off.
David Eun, believed to be a passenger on the aircraft, posted on Twitter: “I just crash landed at SFO. Tail ripped off. Most everyone seems fine. I’m ok. Surreal.”
He added: “Fire and rescue people all over the place. They’re evacuating the injured.”
Federal Aviation Administration spokeswoman Laura Brown said the Boeing 777 was supposed to land on runway 28 left at San Francisco International Airport.
She said the sequence of events was still unclear, but it appeared the plane landed and then crashed.
Sky News Correspondent Tom Parmenter said: “There were large plumes of smoke coming from this plane.
“The tail seems to be the initial problem on landing, and then the fire seems to have started once the plane was on the runway.
“People have been pictured walking away from the wreckage.”
Flights have been diverted to other airports, including Los Angeles.
Debbie Hersman, chairman of the Transport Safety Board, said: “Teams are going to be focused on operations, human performance, survival factors, the airport, airport operations and they are going to be focussing on the aircraft – the systems, the structures and the power plants.
“It’s still too early for us to tell (what happened).
A statement from San Francisco General Hospital said 10 patients from the crash – eight adults and two children – were in a critical condition.
Asiana is a South Korean airline, second in size to the national carrier Korean Air.
It has recently tried to expand its presence in the United States, and joined the oneWorld alliance, anchored by American Airlines and British Airways.