Capt. Adrian Ratushniak says the blaze smouldered for more than 12 hours after a series of explosions sent smoke pouring from grates on a street in the financial district, but crews put out the remains of the fire on Tuesday morning.
He says fire crews will remain on scene as a precaution while hydro crews begin the work of replacing a transformer damaged in the blaze.
There were no injuries in the incident, which began with an initial explosion in a hydro vault shortly after 5 p.m. Monday.
Police block the street as smoke pours into the air following a series of explosions in Toronto on Monday.
Ratushniak says crews initially had to fight the fire with carbon dioxide gas because dumping water on the energized hydro vault would have been dangerous. They were eventually able to extinguish the blaze with water.
Toronto Hydro has said crews would have to pump water out of the vault and dry the equipment before venturing inside to start repairs.
The incident had disrupted transit service in the area, but Toronto transit officials said a subway station returned to operation late Monday and north-south buses along both Yonge and Bay streets were running as usual. The east-west King St. streetcar was still being diverted.