A massive power outage on Thursday night left thousands of residents in Toronto's west end in the dark, while also disrupting public transit service as temperatures in the city were expected to drop to a frigid –20 C.

The outage occurred at around 10 p.m. ET following flooding from a water main at a Toronto Hydro power station, Toronto Hydro spokesman Paul Reesor told CBCNews.ca early Friday.

Power was knocked out in the grid extending from Queen Street to St. Clair Avenue and Spadina Avenue to Jane Street, Reesor said, but he could not give an estimate on when service would be restored.

"Our crews are on the scene in preparation of any restoration," he said. "They have to pump the water out of the station."

The outage forced transit officials to suspend service on Toronto's Bloor-Danforth subway line between St. George and Islington stations, likely for the rest of the night, said Brad Ross, the Toronto Transit Commission's director of corporate communications.

"We can run the trains, but the problem is the lighting in the stations are on the power grid," Ross told CBCNews.ca late Thursday.

Streetcar service in the area has not been affected by the outage, and the TTC has brought shuttle buses into service along Bloor Street, Ross added.