The Special Investigations Unit is investigating after a vehicle collision on Leslie Street in Queensville, York Regional Police say.
An officer attempted to stop a vehicle for speeding around 2:10 p.m., police said. That vehicle then fled and eventually collided with another on the rural stretch of road north of Newmarket.
One person was injured in the collision and was taken to hospital with non-life threatening injuries.
Leslie Street is expected to remain closed for several hours. SIU investigators have yet to reach the scene, police said.
The SIU is an independent civilian agency that investigates interactions between police and the public that result in serious injury or death or allegations of sexual assault.