Italian MotoGP rider Marco Simoncelli died after a horrific crash at the Malaysian Grand Prix in Sepang on Sunday.
Simoncelli, 24, crashed on the second lap and was hit by the bikes of Colin Edwards and Valentino Rossi as he slid across the track on his Honda.
His helmet was knocked off in the incident and the season's penultimate race was stopped immediately with a red flag and then cancelled.
Yamaha's Edwards also came off his bike but escaped serious injury, while Rossi was able to coax his Ducati back to the pits.
Simoncelli lay stricken on the track before being taken to the circuit's medical centre where he was pronounced dead.
"Everybody involved in MotoGP extends its deepest condolences to Marco's family, friends and team at this tragic loss," MotoGP said in a statement.
Casey Stoner, who won his second MotoGP title at his home Australian Grand Prix last week, said: "As soon as I saw the footage it just makes you sick inside.
"Whenever the helmet comes off that's not a good sign."
Medical director Michele Macchiagodena said Simoncelli was already unconscious when medics reached him.
"He was hit by other riders, he suffered a very serious trauma to the head, to the neck and the chest," he said. "In the ambulance there was a cardiac arrest."
Macchiagodena added: "(Edwards) had a dislocation of the shoulder and with anaesthesia the shoulder now is in the correct position. He is fine."
Simoncelli's death is the first in the sport's premier class since another Honda rider, Daijiro Kato, was killed at the 2003 Japanese Grand Prix.
Kato's fellow Japanese Shoya Tomizawa also died in a similar crash to Simoncelli in Moto2, the class below MotoGP, last year.
Simoncelli, known for his shaggy afro haircut and fun-loving personality, began in the 125cc class in 2002 before moving up to the 250cc class in 2006.
He won the 250cc world title in 2008.