Peel Regional Police say they were first called to Derry Road and Ninth Line in Mississauga at 10:38 p.m. Saturday night for a two-vehicle crash.
They arrived to find a 20-year-old man pronounced dead at the scene.
A woman in the same vehicle was rushed to Sunnybrook Hospital in serious condition.
The intersection was closed in all directions for a long time.
About two hours later, at 12:39 a.m., police were called to Creditview Road and Wanless Drive in Brampton for another collision.
They arrived to find that two vehicles had collided and a passenger in one of them had been ejected from the vehicle.
The person who was ejected was pronounced dead at the hospital.
Three other people, including a nine-month-old baby, were taken to hospital trauma centers with serious injuries.
The intersection was closed in all directions for a significant amount of time.
