It took only a few minutes to transform downtown streets into miniature canals. The foul odour of overflowing sewage floated over the area near the port.
Many thousands of people were affected. While some scooped water from their own basements, much larger buildings were evacuated including a fancy downtown hotel, the Quebec provincial library, multiple university pavilions, commercial centres and a large part of the metro system.
More than 28,000 people lost electricity in Quebec, with more than half those disruptions occurring in the province's biggest city. All but about 4,300 customers in the province and 1,900 in Montreal regained their power later in the evening.
The brief but powerful storm saw a sunny afternoon lapse into night-like darkness. A solid slab of water crashed through the air, eventually bursting sideways in what looked like puffy, swirling white clouds.
The rain overwhelmed the city's aging infrastructure in some places, with water pushing up through manhole covers and sometimes lifting them up.
People scrambled through the streets, some screaming as they were pelted and struggling to cling to umbrellas that seemed about to fly out of their hands.
By the time it was over, there were cars partly submerged in what looked like little lakes, while a pool of water covered several subway stations.
Within hours, many of the trouble spots had been cleared and the metro service was restored on the line that had been disrupted.
Environment Canada said between 40 and 80 millimetres of rain had fallen on the city. Federal meteorologist Andre Cantin said it was the kind of event that occurs in a city once every five to 10 years.
At the Place d'Armes metro stop near Old Montreal, the water was ankle-deep at the ground-floor turnstile — which is well above the lower-level tracks.
Would-be commuters said they had arrived there to an improbable sight: a sheet of water spilling onto the turnstile area from the windows above.
"It was raining from the ceiling," said Allyson Haring after she navigated the ankle-deep water around the ticket booth.
Her friend said she had never seen anything like it.
"Up here if it's flooded, I wonder what is going on down there (on the tracks)," said Brenna Maciw, who was scrambling to find another way home to the city's outer suburbs.
"I feel like this is something that's going to go down in the books."
Business people hoping to take the subway skipped, hopped and sloshed through the massive puddles — some while wearing high heels. Upon arriving, they were turned away.
Transit workers, meanwhile, tried to sop up the water with mops and vacuums.
Fire department crews were also dispatched from a number of stations, their heavy engines kicking up water in the streets ahead of them like the bows of ships.
There were also unconfirmed reports of the police 911 system being overwhelmed by calls.
The late-afternoon storm followed a lengthy and loud early morning thunderstorm in the city, and a sunny afternoon. Between those two storms, up to 120 mms had fallen on Montreal, about a third of it coming in the less severe morning shower.
The worst downpour during the afternoon rush hour caused a temporary shutdown of the Ville-Marie tunnel, one of the city's busiest and most important expressways.
A famous Olympic athlete was caught up in the mess.
"Yup," figure skater Joannie Rochette tweeted, "I've just taken a boat tour of the Ville-Marie tunnel!"
There was minor damage at the local CBC building. A spokesman there said floods did not damage the broadcaster's archives.
Concordia University was investigating reports of damage to its library. Classes continued Tuesday evening but some university buildings were evacuated, including the library. Pavilions were also evacuated at UQAM university.
Guests were forced to leave an upscale hotel, Le Crystal, that had been flooded. There were also reports on Twitter that several hundred students at a CEGEP, Dawson College, were forced to evacuate during a major exam.
There were some stomach-churning scenes, too.
The clogged sewers caused dirty water to accumulate in some low-lying neighbourhoods. The local CTV station ran, on its website, a photo supplied by a viewer of a rat swimming on the street.
From a single downtown intersection it was possible to see emergency vehicles zipping off in three different directions, their lights flashing and sirens wailing.
There were no immediate reports of injuries.
-With files by Nelson Wyatt, Jonathan Montpetit and Alexander Panetta
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