TORONTO -- Record-smashing rains knocked out power for hundreds of thousands of residents across the Greater Toronto Area, including the majority of Mississauga, and so badly flooded some roads and major highways that drivers abandoned their waterlogged vehicles.

Mississauga, a city of more than 700,000, saw some of the worst of the blackouts with 80 per cent of the community plunged into the dark, according to power distributor Enersource. By around 10 p.m., only about 50,000 were without power.

Toronto Hydro said about 200,000 customers were still without electricity as of 1 a.m. Tuesday, primarily in the west and northwest parts of the city. The utility could not say when it expected full power to be restored.

Environment Canada said some parts of the GTA had been drenched with more than 100 millimetres of rain, trouncing the previous one-day rainfall record of 29.2 mm in 2008 for Toronto and even beating the 74.4 mm monthly average for July.

Water from flash flooding poured out of sewer drains while Toronto's downtown core was dotted with abandoned vehicles, some sitting in water up to their windows. One woman, sporting a T-shirt and shorts, dove head-first through the window of her marooned car before wading away in the thigh-deep currents.

Drivers were not the only ones dealing with problems getting around after the severe thunderstorm system hit about 5 p.m.

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.

Go Train commuter service was also disrupted after portions of track along the western Lakeshore and Richmond Hill lines were left under water.

A rush-hour train became stranded in floodwaters up to the lower windows as it made its way north to Richmond Hill. The murky brown water spilled through the bottom floor of the carriages and sent riders fleeing for dry ground in the upper sections of the train.

"There's a full-on river on either side of us... We. Are. Stuck. Hard," passenger Jonah Cait quipped on Twitter.

Metrolinx spokeswoman Vanessa Thomas said the power was shut off and windows cranked open for ventilation on the double-decker train.

Commuter Mike Li said the double-decker green-and-white train became stuck in a dipped part of the track and was trying to back out when it became paralyzed by encroaching floodwater.

"People take it for what it's worth, but some are frustrated too," he said.

Police and firefighters used small 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 operation, about seven hours after it began.

Emergency officials said five or six people were treated at the scene for minor injuries during the operations and none required hospitalization.

It was unclear if the Toronto subway system would be in full operation Tuesday morning after an evening of traffic chaos and widespread power outages throughout the city due to record-setting rainfall.

At Toronto's Union Station transit hub, commuter Gilbert Bae worried about flooding in the basement of his Mississauga home as he waited several hours for a GO train back.

"I'm feeling bad," he said. "My wife keeps calling me but I cannot do anything."

Air travellers were also affected. Porter Airlines tweeted at about 7 p.m. that it had cancelled all flights out of the city's downtown airport for the rest of the evening due to power outages in the terminal.

Flooding even claimed Pearson airport's website offline, as its computer server room got soaked by flooding.

PowerStream Inc. said 20,000 customers were knocked off the grid in Markham and Richmond Hill. Later in the evening it said only about 100 in Markham were still without electricity.

The Don Valley Parkway, a major artery, was partly closed as the Toronto Region Conservation Authority said the Don River's banks were at risk of collapse, while provincial police warned drivers to steer clear of parts of Highways 427, 401 and 27, all due to flooding.

Toronto police advised residents to stay at home if possible and avoid driving completely.

-- With files from Clare Clancy