Officers and the ambulance service attended the scene and she was taken to the John Radcliffe Hospital in Oxford with life-threatening injuries where she remains in a critical condition.

The road was closed while officers attended the scene to investigate the circumstances.

Investigating officer PC John Belson, from the Joint Operations Unit for Roads Policing based at Amersham, said: “I am keen to speak to anyone who was in Austenwood Lane near Bull Lane at or around the time of the incident who saw or who has any information which may assist with the investigation.

“We are in the early stages of making enquiries to establish the circumstances which led to the cyclist sustaining the injuries.

“This was a particularly traumatic incident involving a school child on her bicycle. Our thoughts firstly go out to her family at this difficult time. I really wish to hear from anyone who saw what happened to contact me or recalls seeing a cyclist around the time in question.”

Anyone who witnessed the collision should contact the 24-hour Thames Valley Police enquiry centre on 101 quoting URN 1140 27/9.