SAN FRANCISCO, United States (AFP) - A survivor of the San Francisco plane crash on Saturday described the terrifying moments as the Boeing 777 smashed into the ground at the international airport, flinging flight attendants out the back as the tail broke off.

"Right when it appeared to coast for the landing, ... (he) sped up, like the pilot knew he was short," Elliott Stone told CNN.

"And then the back end just hit, and flies up in the air, and everybody's head goes up to the ceiling. And then it just kind of drifts for a little bit, for a good 300 yards and then tips over. Fire starts," he explained.

He said he was able to evacuate safely, sitting in the middle of the plane, but the flight attendants sitting in the back "got hammered - because we landed short.

"And then they all fell out - and it was just the most terrible thing I've seen," Stone said.

He said around 20 minutes after the crash, he and fellow passengers noticed "another five bodies like 457m away that nobody saw," adding they alerted emergency workers, but were frustrated at the response.

"We were yelling at people, yelling at firefighters. Get over here. They were just lagging hard. I don't know." Witnesses on the ground also described watching the Boeing 777 smash hard into the ground.

"We saw it hit, the tail broke off almost immediately upon hitting what appeared to be the end of the runway. It kind of did a bellyflop landing," Jennifer Sorgen told CNN.

"There wasn't a huge explosion of fire, but this was definitely fire, lots of smoke." An airplane mechanic who witnessed the crash from the airfield also saw the smoke.

"It landed straight, then went to the side and then all you saw was smoke coming off it," Adrian John Mirabueno told the San Francisco Chronicle. "I was scared for the families, and to tell the truth I've never seen anything like it." Another onlooker said he did see any fire before the plane hit the runway.

"You heard a pop and you immediately saw a large, brief fireball that came from underneath the aircraft," Anthony Castorani, who saw the flight land from a nearby hotel, told CNN.

Others clarified the plane went into a flat spin around on the ground, as opposed to flipping over.

Helicopter footage showed a trail of debris and blackened pavement starting from the seawall at the very edge of the runway to where the plane finally came to rest in the dirt between the runway and a taxiway.

Amateur pictures and videos of the wreckage were immediately circulating on social media sites, including one from David Eun, a tech executive, who said he survived the crash.

Eun described the immediate aftermath, posting on the Path social media site, "Fire and rescue people all over the place. They're evacuating the injured. Haven't felt this way since 9/11. Trying to help people stay calm.

Deep breaths..." But he soon after posted a more reassuring message, saying "Lots of activity here. Friends, pls don't call right now. I'm fine. Most people are totally calm and trying to let the fire and rescue do their jobs. Just like during 9/11, most people are great and try to be helpful in crisis..."

The plane, Asiana flight 214, was flying from Seoul to San Francisco with 291 passengers and 16 crew members when it hit around 11.30 am local time (2.30am Singapore time).