Canada's national weather service said some parts of the city had been drenched with more than 3.9 inches (10 centimeters) of rain in the Monday evening storm, easily beating the previous one-day rainfall record of 1.4 inches (3.6 centimeters) in 2008.
Toronto police and firefighters used small inflatable boats to rescue commuters from a 10-car, double-decker commuter train that stalled in floodwaters that reached the lower windows. Murky brown water spilled through the bottom floor of the carriages, sending passengers fleeing to the upper decks
A spokeswoman for the Ontario government's transit authority said power was shut off and the windows were cranked opened to provide ventilation. The train was carrying about 1,400 passengers during the Monday evening rush hour.
"There's a full-on river on either side of us... We. Are. Stuck. Hard," passenger Jonah Cait wrote on Twitter.
Another passenger told the TV news network CP24 that she could see people clinging to trees after abandoning their cars on a flooded highway alongside the tracks.
Police and firefighters used the inflatable boats to ferry all 1,400 passengers a short distance to higher ground. It took until about 12:30 a.m. to complete the rescue operation, about seven hours after it began. Passengers were transported to a nearby subway station to resume their trip home.Emergency officials said five or six people were treated at the scene for minor injuries, but no one required hospitalization.
Ontario's regional public transit service said early Tuesday that the storm had left portions of track "completely under water" on several lines. It said the extent of the damage to the tracks was not yet known, but expected service Tuesday morning "to be impacted" and suggested passengers seek alternative ways to travel.
All of Toronto's subway service was temporarily halted due to power and signal issues. Some stations were also flooded. Partial service later resumed but large parts of the system were still shut down. It was unclear if the subway system would be in full operation by Tuesday morning.
The storm left the downtown core dotted with abandoned vehicles, some sitting in water up to their windows. One woman, in a T-shirt and shorts, dove head-first through the window of her marooned car before wading away in the thigh-deep currents.
Porter Airlines canceled all flights out of the downtown airport due to power outages in the terminal Monday evening. It was not clear how many flights were affected.
Local electric company Hydro One said about 300,000 people in the west end of the Greater Toronto Area were without power due to "significant flooding" at two transmission stations. The utility said although 30,000-to-40,000 people had their power restored, the amount of flooding was impacting its ability to complete the repairs.
Toronto Hydro said on its Twitter page that approximately 35,000 of its customers remained without power early today, mainly in the west end. The utility said it was awaiting supply from Hydro One and that it could be as late as mid-morning before all of its customers had their electricity restored.
Toronto's flash flooding comes two weeks after extensive flooding in Calgary turned parts of the western Canadian city into a lake and forced up to 100,000 Albertans from their homes. Three bodies were recovered during the floods.