Federal Aviation Administration spokeswoman Laura Brown said Asiana Airlines Flight 214 crashed while landing on runway 28 left at 11:26 PDT.
Television footage showed the top of the fuselage was burned away and the entire tail was gone. One engine appeared to have broken away. Pieces of the tail were strewn about the runway. Emergency responders could be seen walking inside the burned-out wreckage.
Stephanie Turner saw the plane going down and the rescue slides deploy, but returned to her hotel room before seeing any passengers get off the jet, she told ABC News. Turner said when she first saw the flight she noticed right away that the angle of its approach seemed strange.
"It didn't manage to straighten out before hitting the runway," she said. "So the tail of the plane hit the runway, and it cartwheeled and spun and the tail broke off ... I mean we were sure that we had just seen a lot of people die. It was awful."
The National Transportation Safety Board said it was sending a team of investigators to San Francisco to probe the crash. NTSB spokesperson Kelly Nantel said Saturday that NTSB Chairman Deborah Hersman would head the team. An FBI spokesperson said there is no indication that terrorism was a factor in the crash. The FBI will assist the NTSB in its investigation.
Asiana is a South Korean airline, second in size to national carrier Korean Air. Flight 214 originated in Shanghai before stopping in Seoul on its way to San Francisco.
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.
Of the 291 passengers on board, including 19 in business class and 272 in travel class, 77 were Korean citizens, the airline said. Another 141 were Chinese citizens, 61 were U.S. citizens and one was a Japanese citizen.
Prior to Saturday's crash there had never been a fatality on a Boeing 777 since the aircraft type was first introduced in the late 1990s.
The last time a large U.S. airline lost a plane in a fatal crash was an American Airlines Airbus A300 taking off from John F. Kennedy International Airport in New York in 2001.
National Transportation Safety Board chairman Deborah A.P. Hersman and other NTSB officials are to board a plane from Washington, D.C. to San Francisco to investigate the crash.
San Francisco General Hospital is treating 52 people, including at least two children. Five of the patients are in critical condition.
Twelve people were transported to Mills Peninsula Medical Center. Two were admitted, two were discharges and eight people are under observation. All are in stable condition.
Stanford has seen 45 patients for evaluation and treatment.
Officials weigh in on crash
President Barack Obama was made aware of the crash by Lisa Monaco, Assistant to the President for Homeland Security and Counterterrorism shortly after it occurred. The White House says he is monitoring the situation.
The White House issued a statement saying in part, "[Obama's] thoughts and prayers go out to the families who lost a loved one and all those affected by the crash."
Gov. Jerry Brown issued a statement saying, "Anne and I extend our deepest concerns and sympathy to the passengers who were aboard Asiana Flight 214 and to their families. We are grateful for the courage and swift response of the first responders whose actions surely prevented an even greater tragedy."
Mayor Ed Lee participated in press briefings from SFO and issued a statement saying, "The passengers and their families remain our first priority, and we will continue to provide them with the support they need."
House Minority Leader Nancy Pelosi also issued a statement on the crash, saying, "No words can console those who lost loved ones in this terrible tragedy. All of San Francisco shares in their shock and grief."
Facebook COO Sandberg changes flight
Facebook COO Sheryl Sandberg posted to her Facebook page that she was supposed to be on the Boeing 777 that crash along with some of her family and colleagues.
She posted on her Facebook page, "We switched to United so we could use miles for my family's tickets."
Samsung executive survives crash
Samsung executive David Eun was on Flight 214 and escaped without injury. He used Twitter throughout the ordeal to update what was going on inside the plane and at the airport.
Two runways reopened around 3:30 p.m., according to a tweet from SFO.
The Associated Press, ABC7 News, and Bay City News contributed to this report.