Fire crews were spotted attending to a blaze underneath the Gardiner Expressway on Saturday afternoon.
Authorities were initially called about an encampment fire near Spadina Avenue and Lake Shore Boulevard West just after 1:00 p.m.
While an investigation is still ongoing, Toronto Fire Services have ruled out the encampment as the cause of the blaze. No injuries were reported.
Footage taken by CityNews in the downtown core appears to show a plume of smoke rising from underneath the highway.
Authorities say the fire has been extinguished and crews will remain on scene to clear the smoke.
The westbound Gardiner Expressway was completely closed at Spadina Avenue for approximately one hour and reopened around 2:15 p.m. However, Toronto police say the ramp on to the westbound Gardiner at Spadina Avenue will remain closed for an extended time.