An investigation has begun into how a disabled girl suffered a broken thigh on a bus taking her to a special needs school.

Rebekh Smith, who has cerebral palsy and is unable to talk, was travelling to the Kingfisher School, in Radley Road, Abingdon, when the bus made a sudden halt.

The wheelchair in which she was sitting broke loose from floor clamps and Rebekh, who had a hip operation two years ago, was catapulted forward into a seat.

No other pupils on the bus were hurt.

At first it was thought that Rebekh, 10, from Great Western Drive, Didcot, had a badly bruised leg, but an examination at Oxford's John Radcliffe Hospital revealed her left thigh bone was broken.

Rebekh's grandmother Penelope Weald said: "She has been through hell with the pain.

"It's all very distressing for Rebekh who is being cared for at home by her mother and father.

"The bus drivers are very careful so there must have been a good reason for the bus to come to a sudden halt. What we cannot understand is how the wheelchair managed to come loose from its floor clamps."

The investigation will focus on the restraining floor clamps that lock the wheels in place and whether the wheels had been secured.

John Sear, fleet operations manager for Oxfordshire County Council, said: "There was an incident in which a student's wheelchair became detached from its fittings in the vehicle, causing injury to the young woman. We are carrying out an investigation to establish all the circumstances."

Steve Gillow, headteacher of Kingfisher School, said: "We were sorry to learn about the accident to one of our pupils.

"All the circumstances are not clear at this stage and the county council is carrying out an investigation to try to establish the facts."