The mate of a teenage motorcyclist in hospital after being run over by a police car in Adelaide has said the pair were "just riding around" and keeping to the speed limit.

The 17-year-old boy is being treated for several broken bones after the incident, which is the subject of an official investigation.

A friend of the injured boy, Brodie Mewett-Sweet, said they were both riding their motorbikes when an officer stopped them.

He said the policeman seemed to have accidentally hit the accelerator in his patrol car, leading to his friend being hurt.

"The cop car just went straight over the top of him — just full acceleration, taking him onto the kerb," he said.

"Then [the officer] stopped the car on the side path, and the ambulance and stuff was called."

Mr Mewett-Sweet said his mate was lying on the ground in obvious pain until ambulance officers arrived at the scene to take him to hospital.

"He's in hospital, apparently he's stable — they said he had two broken femurs and a cracked pelvis," he said.

"They told us the police were called apparently because someone made a complaint we were racing up and down the street, which wasn't the case.

"We were riding around this general area, doing the speed limit, just riding around."

Police describe incident as 'regrettable'

At a media conference on Monday afternoon, police said the officer involved could face charges but the incident was most likely a "terrible accident".

"There's always a possibility that he will face charges but from what I understand it was just a terrible accident," Superintendent Anthony Fioravanti said.

"Our thoughts are currently with the rider and his family.

"It's a regrettable incident, our officers will be speaking to the boy at a suitable time."