SAN FRANCISCO — An Asiana Airlines flight from Seoul, South Korea, crashed while landing at San Francisco International Airport on Saturday, forcing passengers to jump down the emergency inflatable slides to safety. It was not immediately known whether there were any injuries.

The Boeing 777 was supposed to land on runway 28 left at the airport, said Federal Aviation Administration spokeswoman Laura Brown. She said the sequence of events was still unclear, but it appeared the plane landed and then crashed.

A video clip posted to YouTube shows smoke coming from a silver-colored jet on the tarmac. Passengers could be seen jumping down the inflatable emergency slides. Television footage showed debris strewn about the tarmac and pieces of the plane lying on the runway.

Fire trucks had sprayed a white fire retardant on the wreckage.

A call to the airline seeking comment wasn’t immediately returned.

Asiana is a South Korean airline, second in size to 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.

The 777-200 is a long-range plane from Boeing. The twin-engine 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. The airline’s website says its 777s can carry between 246 to 300 passengers.

The last time a large U.S. airline lost a plane in a fatal crash was an American Airlines Airbus A300 taking off from JFK in 2001.

Smaller airlines have had crashes since then. The last fatal U.S. crash was a Continental Express flight operated by Colgan Air, which crashed into a house near Buffalo, N.Y. on Feb. 12, 2009. The crash killed all 49 people on board and one man in a house.

Associated Press writers Joan Lowy in Washington, D.C., and Scott Mayerowitz in New York contributed to this report.

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