AN internal police investigation has begun after a police car on patrol may have been involved in a crash that left a Pilbara woman with serious leg injuries.

The major crash unit is looking into the incident, which occurred at about 7.40pm on Thursday at the intersection of Wise Terrace and McLarty Boulevard in South Hedland.

Police officers were patrolling the area in a car as part of normal duties when they felt a bump. Believing they had struck a kerb, the officers continued driving.

But about one minute later, another police car also patrolling the area found a woman injured and lying on the road.

An officer gave her first aid and she was taken to hospital with suspected fractures to her legs.

She remains in hospital in a serious but stable condition.

Internal Affairs Unit will oversee the investigation and officers from the major crash unit are heading to South Hedland on Friday.