The road remains closed after a blue Nissan Micra and a silver Land Rover Discovery collided just before 8am today between Chazey Heath and Cane End.
The female driver of the Nissan has been flown to the John Radcliffe Hospital by air ambulance in a life threatening condition.
Two adults who were in the Land Rover have been taken to the Royal Berkshire Hospital by road ambulance in a non-life threatening condition.
Emergency services remain on the scene and the road has been closed to through traffic.
Diversions are in place but long delays are expected throughout the morning.
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