Cleveland Police are to refer a crash involving a marked police car in Hartlepool to the Independent Police Complaints Commission (IPCC).
Three people, including the driver of the patrol car, were taken to hospital after it was in collision with a Peugeot in Elwick Road on Tuesday.
The force of the impact sent the Peugeot crashing into a church wall.
A 79-year-old man who was a passenger in the Peugeot is in hospital being treated for a fractured chest bone.
Others injured in the crash were released from hospital after treatment.
The police car was answering an emergency call and witnesses reported seeing the vehicle's blue lights on.