U.S. investigators say the Korean jetliner that crashed Saturday at San Francisco airport was flying "significantly below" its target speed as it approached the runway, and that the pilot tried to abort the landing.
National Transportation Safety Board chair Deborah Hersman spoke to reporters Sunday afternoon. She said the verbal "abort" request came just 1.5 seconds before impact - too late to avoid the crash that killed two people and injured dozens more.
Seconds earlier, she said, "engine stall" warnings sounded in the cokpit.
San Francisco's fire chief, speaking earlier Sunday, said 19 people remain hospitalized, six of them in critical condition.
The two passengers killed were identified as 16-year-old Chinese girls who were among a group of 30 students and their teachers headed to a summer camp from east China's Zhejiang province.
The Asiana flight originated in Shanghai and stopped in South Korea before heading to San Francisco.
Witnesses say the plane's tail appeared to hit first as it sought to clear a sea wall at the base of the runway. After the crash, much of the cabin burned through and debris was scattered along the runway.
Asiana Airlines officials say there is no indication of mechanical problems with the plane or its engines at the time of the crash.
Asiana is South Korea's second largest airline after national carrier Korean Air.
The U.S. Federal Bureau of Investigation says there is no indication the accident was linked to terrorism. The FBI will work with the NTSB, Korean investigators and Boeing as the probe unfolds.
President Barack Obama expressed his condolences to the victims and their families, as did Chinese President Xi Jinping. Chinese media say Xi also ordered Chinese diplomatic missions to do everything they can to help the survivors.
In 2008, a British Airways Boeing 777 jet crash-landed short of the runway at London's Heathrow Airport, but all on board survived.