Italian motorcyclist Marco Simoncelli has been tragically killed in a crash during today's Malaysian Moto GP, race organisers have confirmed.
The Gresini Honda rider lost control of his bike on the second lap of the circuit in Sepang and appeared to be hit by Colin Edwards and then Valentino Rossi as he slid across the track.
The fatal incident comes just a week after British IndyCar racing driver Dan Wheldon died after crashing in Las Vegas
The 24-year-old's helmet came off in the collision and he was taken to the medical centre for treatment, but his injuries were too serious.
A message on the MotoGP website read: 'Marco Simoncelli succumbed to injuries sustained in Malaysia.'
Newly-crowned champion Casey Stoner admitted watching the accident made him worried for Simoncelli, who was later pronounced dead.
'As soon as I saw the footage it just makes you sick inside,' the Australian told BBC2.
'Whenever the helmet comes off that's not a good sign.'
Tony Elias, Moto2 world champion, said he was praying the injuries to Simoncelli were not serious before learning the devastating news.
'We just hope Marco is OK - that's my wish,' he said.
The organisers confirmed the race was cancelled, having halted it immediately after the fatal incident.
The Gresini Honda rider lost control of his bike on the second lap of the circuit in Sepang and appeared to be hit by Colin Edwards and then Valentino Rossi as he slid across the track.
The fatal incident comes just a week after British IndyCar racing driver Dan Wheldon died after crashing in Las Vegas
The 24-year-old's helmet came off in the collision and he was taken to the medical centre for treatment, but his injuries were too serious.
A message on the MotoGP website read: 'Marco Simoncelli succumbed to injuries sustained in Malaysia.'
Newly-crowned champion Casey Stoner admitted watching the accident made him worried for Simoncelli, who was later pronounced dead.
'As soon as I saw the footage it just makes you sick inside,' the Australian told BBC2.
'Whenever the helmet comes off that's not a good sign.'
Tony Elias, Moto2 world champion, said he was praying the injuries to Simoncelli were not serious before learning the devastating news.
'We just hope Marco is OK - that's my wish,' he said.
The organisers confirmed the race was cancelled, having halted it immediately after the fatal incident.
Deadly: The rider (No 58) is seen sliding from his bike and colliding with two other riders in a horrifying crash
Moment of horror: Simoncelli loses control on the secon
Disaster: Simoncelli fatally falls off of his Honda after colliding into Colin Edwards
Fall: Edwards spins off the track along with Simoncelli's bike as the 24-year-old Italian devastatingly lies motionless
Race marshalls attend to Honda rider Simoncelli (C) following his fatal crash just four minutes after the start of the Malaysian MotoGP race
Devastated: Colin Edwards of the US who was involved in the crash stands at the side of the track after the fatal crashA bulletin from the organisers, reported on website Autosport, said: 'Race cancelled as the medical centre staff is focusing on treating Marco Simoncelli and track action cannot be resumed in the current circumstances.'
It was confirmed on MotoGP's official website that he died at 4.56pm local time.
Tributes came in pouring in from his fellow riders soon after the incident.
British MotoGP rider Cal Crutchlow wrote on Twitter: 'RIP Marco Simoncelli ! A great rider and all round nice guy. My thoughts are with all his family & friends. I will never forget today.'
Agony: Marco Simoncelli's father is comforted as he waits outside a medical centre where the rider was taken following a crash at the Malaysian Grand Prix
Crew members of the Honda team of Marco Simoncelli of Italy console each other as they gather outside a medical centre where the rider was taken following a crash at the Malaysian Grand Prix 
Wheeled away: Track officials remove Simoncelli's motorcycle after the dreadful accidentLast week British IndyCar racing driver Dan Wheldon died after he was catapulted helplessly into the air in a 225mph smash before landing on a barrier and suffering fatal head injuries.
Just days earlier the father-of-two joined a number of other drivers in expressing the fears over the speed of cars and overcrowding on the oval-shaped track.
But in a blog post, he had promised fans he would go out to win and put on a show of 'pure entertainment'.
The organisers cancelled the race when the extent of Simoncelli's injuries become apparent, having halted it immediately after the accident