Montreal police Const. Simon Delorme said witnesses saw a car go through a red light and collide with another car.
The impact of the collision apparently sent the vehicle skidding in the opposite direction.
That's when it hit a pedestrian, who was sent flying underneath a parked car.
Police said the victim is in critical condition.
Both drivers and their two passengers are also being treated in hospital for their injuries, which range from minor to serious.
The driver of the parked car was treated for shock.
Investigators are on the scene to gather more information.