A woman has been left with spinal injuries after being struck by a police car patrolling a northern NSW town.

The police sergeant behind the wheel of the fully marked police car had been looking out for a stolen vehicle when the collision happened in South Kempsey about 2.20am on Friday.

Early indications were that the car was not under lights and sirens, and the officer had not seen the stolen vehicle he was looking for, Assistant Commissioner Peter McKenna said on Friday.

The car’s speed at the time of the collision would form part of the internal police investigation, he said.

The male officer driving the sedan returned a negative roadside breath test.

The local woman, unlinked to the investigation, was on the roadway at the time she was struck.

She was treated for leg, pelvis and spinal injuries by paramedics before being taken to the local hospital and then the higher-acuity John Hunter Hospital in Newcastle.

The 39-year-old is in a serious but stable condition. Her injuries are not believed to be life-threatening, McKenna said.

Out-of-area police will investigate the circumstances surrounding the incident, with oversight from the police watchdog.

Investigators are appealing for any witnesses or footage, such as from dashcams, around the time of the incident.

-AAP