A man has been airlifted to hospital following a collision between a car and a tree on the A413 near Lillingstone Dayrell.
Thames Valley Police were called at 8am to reports of a single vehicle accident involving Citroen C4 which had left the road.
There were four occupants in the vehicle and one of them has been airlifted to the John Radcliffe Hospital, in Oxford.
Fire crews from Buckingham and Winslow attended the scene as well as the air ambulance.
Firefighters are expected to be leaving the scene shortly.
The vehicle is still on the scene and is waiting to be recovered.