In the second fatality to hit motorsport in a week following the death of the British driver Dan Wheldon at the Las Vegas Motor Speedway, Simoncelli appeared to lose control on the second lap at Sepang, veering into the path of the American Colin Edwards and Italy's Valentino Rossi.

Simoncelli, 24, who lost his helmet during the crash, was left lying motionless on the track with tyre marks visible on his neck. The Gresini Honda rider and former MotoGP champion died within an hour of chest, head and neck injuries.

"When our medical staff got to him he was unconscious," said MotoGP's medical director, Dr Michele Macchiagodena. "In the ambulance because there was a cardiac arrest they started CPR [cardiopulmonary resuscitation]."

As the race was cancelled and silence fell at the track, doctors worked to remove blood from Simoncelli's thorax and continued to perform CPR for 45 minutes, but failed to revive him, said Macchiagodena. Edwards suffered a dislocated shoulder in the crash but Rossi was unharmed.

After Simoncelli's death was announced – the first fatality in MotoGP since Japan's Daijiro Kato crashed at the 2003 Japanese Grand Prix – tributes immediately poured in for the rider renowned for his afro-style curly hair, jokey personality and aggressive riding technique.

"I'm so shocked and saddened by the loss of Marco," said the MotoGP champion, Casey Stoner. "When things like this happen it reminds you how precious life is, it makes me feel sick inside."

The Repsol Honda rider Andrea Dovizioso said: "I watched the images and I'm shocked. In a race you fight and push hard and disaster is often around the corner. Marco was a strong rider and he always pushed hard. We raced together since we were kids, I saw him always pushing to the maximum, he crashed many times, but without major injuries, he seemed invincible. What happened today seems impossible."

Simoncelli, from Emilia-Romagna in central Italy, rode motorbikes from the age of seven, taking the Italian Minimoto title at 12. In 2008 he won the 250cc world championship with Gilera before finishing eighth in his debut MotoGP season with Honda last year.

Popular with fans thanks to his good looks, Jimi Hendrix T-shirts and wild hair which forced him to wear a helmet one size larger, Simoncelli's enthusiasm for motorsport – he once said he would race for free or even pay to do to it – won him friends including his fellow Italian rider Rossi, who was in tears at the track in the long minutes before the announcement of his compatriot's death.

At more than 6ft, Simoncelli looked cramped on his bikes, his elbows appearing to graze the track on turns, and his extra weight pushed him into aggressive starts to make up lost seconds. That aggression did not always endear him to other riders. "We are riding at 300 kilometres per hour with a very powerful and very heavy bike," said Jorge Lorenzo after criticising Simoncelli's style this year. "It's not mini-bikes. It's a dangerous sport and you have to think about what you do."

In May Simoncelli collided with Dani Pedrosa in the French GP, after which he conceded he needed to show more caution. On Sunday Pedrosa said. "In a tragedy like this there is not much to say. I just want to give my condolences to his family and all the people who love him. I've been with his father and all we could do was to hug, nothing else matters."