Ontario's police watchdog is looking for witnesses after a fatal collision on the weekend.

At 2 a.m. Sunday, a provincial police vehicle collided with a tractor trailer on the Kenora bypass.

The Special Investigations Unit said officers were transporting a 42-year-old woman in custody to the Kenora detachment when their cruiser collided with a tractor trailer (at Highway 17 and Redditt Road).

The SIU said the woman died as a result of the collision, while the officers and the driver of the tractor trailer did not suffer serious injuries. Investigators are asking the driver and any passengers of a dark-coloured pickup truck who may have seen the incident — or events leading up to it — to come forward.

An autopsy is scheduled to occur within the next few days.

SIU spokesperson Monica Hudon said the family of the victim has asked that her name not be made public.

The SIU is an arm's-length agency that investigates reports involving police where there has been death, serious injury or allegations of sexual assault.

With files from Canadian Press