Ontario Provincial Police are still working to confirm the identities of four of the five victims of a multi-vehicle highway accident over the weekend in northwestern Ontario.

The four men were all riding in a westbound pickup truck that collided with an eastbound tractor-trailer on Highway 17, about 15 kilometres east of English River, just before 11 pm on Saturday.

Investigators do not believe the four men were residents of northwestern Ontario, a police spokesperson told CBC News on Monday.

The driver of the tractor-tractor, 43-year-old Sukhwinder S. Thandi of Cambridge, Ont., was also killed in the collision.

Police say post-mortem examinations of the four unidentified victims will be conducted in Toronto, but are not sure when.