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 boats to rescue commuters from a 10-car, double-decker train that stalled in floodwaters that reached up to the lower windows. Murky brown water spilled through the bottom floor of the carriages, sending passengers fleeing to the upper decks.
A Metrolinx spokeswoman said power was shut off and the windows were cranked opened to provide ventilation. The train was carrying about 1,000 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.
Metrolinx said the Toronto police marine unit floated out in rescue boats to pull weary passengers through the windows about three and a-half hours after the train got stuck.
The rescue operation continued past midnight. Police constable Wendy Drummond said between one quarter and one half of the passengers had been ferried to shore in inflatable boats by midnight. She said they were being transported to a nearby subway station to resume their trip home.
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.
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.
As many as 300,000 Toronto Hydro customers lost power. Hydro spokeswoman Tanya Bruckmueller said efforts to restore power to customers might be slowed as night fell.
Another utility, Enersource, said power was cut to about 80% of Mississauga, a suburb of 700,000 west of Toronto. By around 10pm, only about 50,000 were without power.
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.