A cable fault in a hydro vault underground slowed down traffic on Yonge Street on Saturday morning.
Toronto police and fire services responded to a call just before 11 a.m. in the Yonge and Carlton Streets area.
A loud blast was reported and police said smoke was coming out of a subway grate.
The sidewalk was cordoned off and one lane of traffic was blocked on Carlton, slowing down streetcar service in the area. Subway service was not affected.
Toronto Hydro says the smoke could have been caused by a cable fault. There were no related power outages and no injuries were reported.