Police are looking for suspects after a motorcycle passenger was killed on Highway 401 Friday night, moments after police signalled for the bike to pull over.

Police say that a Durham Regional Police officer tried to pull over the motorbike at about 11:39 p.m. in the westbound lanes of the highway, just west of Brock Street in Whitby.

Instead, the driver of the motorcycle accelerated and the passenger fell off the back of the bike before being fatally struck by at least one vehicle, said OPP Const. Graham Williamson.

"The motorcycle accelerated (and) the passenger for the motorcycle became dislodged and fell onto the ground. The motorcycle continued on and the passenger was then struck."

Despite being hit by what appears to be multiple cars, no one in the westbound lanes of traffic stopped to help the victim. Police are looking for the driver of the bike and of the vehicles involved in the collision.

The victim, who has not been identified, was pronounced dead at the scene.

Investigators are now trying to determine how many vehicles "made contact with the deceased on the roadway," according to an OPP media release.

Anyone with information about the incident is asked to call OPP investigators at 1-888-310-1122.

The OPP media release says the province's Special Investigations Unit "has invoked its mandate in this incident."

The SIU website says that it "investigates circumstances involving police and civilians which have resulted in serious injury, including sexual assault, or death."

The westbound 401 lanes were shut for nearly 12 hours before reopening on Saturday afternoon.