Four people were taken to hospital following a two-vehicle crash on the westbound Gardiner Expressway.
The collision happened around 3:30 a.m. Wednesday on the westbound lanes between South Kingsway and Islington.
Const. Clint Stibbe of Traffic Services said a vehicle was attempting to re-enter the highway from the shoulder when it was struck by another car.
Toronto paramedics said four people were taken to hospital, one with critical injuries and the other three with non-life-threatening injuries.
The westbound lanes of the Gardiner were closed during the morning rush hour for the collision reconstruction. The highway reopened just before 8 a.m.
Police are asking anyone with information on the crash or have dashcam video of the incident to call 416-808-1900 or Crime Stoppers at 416-222-TIPS.