Toronto hydro spokesperson Denise Attallah said the company restored power to roughly half the affected customers in the morning, but couldn't say when full service would return.
"It could be 18 to 24 hours from 10 p.m. last night," the time the power station was shut down, she said.
The outage shut down the Bloor-Danforth subway line and forced the closure of dozens of schools.
Subway service has now been extended to Keele station from the west and Bathurst station continuing eastbound on the Bloor-Danforth line.
Shuttle buses continue to run between Keele and Bathurst stations.
Even as the subways slowly returned to life, people crowded around bus stops along Bloor to squeeze aboard the coveted shuttles.
Some pushed and elbowed for a spot, eager to warm up after a long and bone-chilling wait.
Meanwhile, with the morning rush in full swing, many commuters wondered if they should just head back home.
"It's Friday, I don't really want to work today," said Jennifer Lightbody, 25, as she mapped an alternate route from Dufferin to her job near Leslie station.
"I'm hoping I can go home, sleep some more," said Lightbody, whose apartment was plunged into the dark and cold last night. "I don't have heat, but I have cats - they're like little heating pads."
Power went out in most of the Jane St. to Spadina Ave. and Queen St. to St. Clair Ave. areas around 10 p.m. last night, said Staff Sgt. Devin Kealey.
"We've got all sorts of grief. Traffic lights, houses, everything," Kealey said. Police have called in extra units to patrol intersections, he said.
All schools in the affected area are closed for the day. Click to find out which Catholic and public schools are closed.
In response to the blackout, the city has opened reception centres where residents without power can go for warmth.
All community and recreation centres, libraries and daycare centres in the affected area are closed. Any libraries or recreation centres that have power are also welcoming residents seeking warmth.
Toronto Hydro said it expects the outage, which affected about 22,000 customers, to last until at least 4 p.m. and advises residents without power to seek shelter with a friend or family.
The flooding occurred in the basement of the Toronto Hydro facility on Dufferin St., just north of Bloor St., short-circuiting the power system.
Crews removed a lot of water from the flooded station and are now drying equipment to assess the damages, she said.
Crews worked throughout the night, but were unable to get the power back on. Temperatures dropped overnight to around -20 C.