Factory KTM rider Acosta was leading the 24-lap race when his RC16 suddenly slowed between Turn 9 and 10.
Acosta raised his hand, but not in time for Marquez to react. With nowhere to go, he slammed into the back of the preceding KTM RC16.
Marquez and his Ducati Desmosedici went cartwheeled through the grass, scattering debris across the course.
Marquez was taken to the infield medical centre before being transported to a nearby hospital.
VR46 rider Fabio Di Giannantonio was an innocent casualty of the melee as he hit one of Marquez’s stray wheels that came back onto the track.
Acosta was able to return to the pits with assistance from fellow competitors.
Race control confirmed a race restart following a lengthy clean-up with the grid set by the order at the end of the previous lap.
Pit exit opened at 10:48pm AEST for a 13-lap race with Acosta alongside Trackhouse rider Raul Fernandez and Jorge Martin of Aprilia.
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