The Malaysian Grand Prix has been cancelled after an accident involving Gresini Honda's Marco Simoncelli.
There has been no official news on Simoncelli's condition, but organisers took the decision to cancel the race following a crash on lap two.
A bulletin from the organisers said: "Race cancelled as the medical centre staff is focusing on treating Marco Simoncelli and track action cannot be resumed in the current circumstances."
The Italian had been fighting with Alvaro Bautista for fourth when he lost the front of his bike and slid across the track, into the path of Colin Edwards and Valentino Rossi, both of whom appeared to hit the Honda.
Edwards was able to walk away from the crash but suffered a dislocated shoulder, while Rossi able to continue.
Concern centres on Simoncelli, who lay stricken on the track, his helmet having come off during the incident.
He was taken by ambulance to the circuit's medical centre.