(UPDATE) According to Reuters, one of the two Chinese girls who died may have been run over by an emergency vehicle. According to another Reuters article, this was the very first landing on San Francisco Airport on Boeing 777 for the Asiana pilot, who was training on 777 with 43 hours so far. The co-pilot who had significantly more hours (3,220) on 777 and overall was assisting the pilot.
In an CNN interview, an American on board Asiana Flight 214 said ambulances didn't come for more than 20 minutes, and when they did, the crew ignored his word that there were people behind the plane who fell out of the back of the plane.
That's where the girls were.
Just heard on the radio news: the plane was coming in at a speed significantly lower than the speed for landing. So the plane stalled.