A Boeing 777 operated by Asiana Airlines crash-landed on Saturday afternoon at San Francisco International Airport (SFO). Two fatalities have been confirmed thus far, with an airport spokesperson stating that 182 individuals have been sent to local hospitals for treatment. The flight, which originated in South Korea, had 291 passengers and 16 crew members on board.

The cause of the accident is unknown and will likely take some time to investigate, but it's notable that the 777's only other major failure — a downed British Airways aircraft at London Heathrow — crashed under similar circumstances on final approach, resulting from a clogged fuel filter that has since been redesigned and retrofitted on existing aircraft using Rolls Royce's Trent 800 series engines. This particular aircraft was powered by a different engine, the PW4000.

Almost immediately following the incident, dozens of tweets began flowing with news and firsthand accounts from the airport — including some from Samsung executive David Eun, who said he was aboard the aircraft. He called the experience "surreal" while reporting that "most everyone seems fine." Several pictures of the 777 show the vertical stabilizer completely missing, emergency slides deployed, and black smoke billowing above.

The National Transportation Safety Board has released further photos of the crash on Twitter.

Update: Officials are saying there's no way to know yet what caused the accident, but CNBC and others are reporting that the plane came in too short for its landing, and its tail hit the seawall at the end of the SFO runway.

Update 2: SFFD chief Joanne Hayes-White has confirmed that there are two fatalities associated with the crash. During a press conference with the FBI and SF Mayor Edwin Lee, Hayes-White said repeatedly that answers are still a long way out.

Update 3: Asiana Airlines has identified the dead passengers as Ye Mengyuan and Wang Linjia, both 16-year-old students from China.

Update 4: More details have emerged surrounding the crash — it's possible that crew error led to the crash, not a mechanical failure. For all of the latest news, please read this story.