Italian motorcyclist Marco Simoncelli has been 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 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."
It was confirmed on www.motogp.com that he died at 4.56pm local time. The organisers cancelled the race when the extent of Simoncelli's injuries become apparent, having halted it immediately after the accident.
Newly-crowned champion Casey Stoner admitted immediately after the crash he had feared the worse.
"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."
Tributes came in from his fellow riders.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."
Simoncelli, who won the 250cc world championship in 2008, clinching the crown in Sepang, stepped up to MotoGP in 2010. His death was the first fatality in MotoGP since Japan's Daijiro Katoh died from his injuries sustained at the 2003 Japanese Grand Prix.
And it comes exactly a week after British racing driver Dan Wheldon, a former IndyCar champion and two-time Indy 500 race winner, was killed in a 15-car pile-up at the Las Vegas Motor Speedway.