The news is just breaking now, but an Asiana 777 from Seoul has crashed while landing at San Francisco International Airport. No injuries reported at this point, but one passenger tweeted:
plane came in at a bad angle, flipped, exploded.
But other reports differ. David Eun (@Eunner) has tweeted the following:
Fire crews are on the scene and the aircraft is sitting on its belly with the nose pointed slightly upward. Passengers have been sighted alighting from the aircraft.
I will provide an update as more details become available.