Durham Regional Police are investigating a fatal collision in Ajax on Friday afternoon.
The crash occurred on Taunton Road West and Harwood Avenue North at around 3 p.m.
Police said two people were transported to trauma centres in Toronto with life-threatening injuries.
A short time later, police said the crash had turned fatal, but they did not confirm the number of people who died.
The cause of the crash is unknown.
Police have closed Taunton Road West between Westney Road and Middlecote Drive for investigation.