Police say a minivan and a pickup truck collided head-on. A car then hit the other two vehicles.
The accident happened at about 6 a.m. near the intersection of Bathurst Street and Highway 11.
The driver and the passenger in a van — both aged 27 — were rushed to hospital with critical injuries. Both later died.
Police have not released the names of the victims.
The driver of a truck and the driver of a car were also injured in the collision. Their injuries were minor.
Police said weather conditions may have been a factor in the accident.
Sgt. Gary Phillips told CBC News it was extremely foggy in the area at the time of the accident, with visibility down to about one metre.