after horrific crash
Both riders appeared to hit Simoncelli, whose helmet came off during the incident.
The race was red flagged immediately, and cancelled a few minutes later when it emerged that Simoncelli was in a critical condition.
Honda rider Simoncelli was in his second season in MotoGP, and established himself as a fan favourite with his flamboyant riding style.
He took his maiden podium spot in the series in the Czech Republic two months ago, and followed that up with a second place finish at the recent Australian Grand Prix.
Simoncelli's death is the second casualty in the top level of motorsport, coming just a week after British driver Dan Wheldon was killed in an IndyCar race in Las Vegas.