Nearly half a million homes were in the dark on Friday as remnants of tropical storm Debbie wreaked havoc in southern Quebec.

In Montreal, many roads were flooded, basements were submerged, and the city's light rail network, REM, was completely shut down due to the power outage as heavy rainfall hit the area.

Environment and Climate Change Canada (ECCC) stated that over 150 mm of rain had fallen by 9 PM, just as the rainfall warning in the area ended. This broke the all-time daily record set in 1996.

Montreal averages 94 mm of rain throughout the month of August.

As of 10 PM, Hydro-Québec reported power outages affecting over 460,000 customers. The hardest-hit areas were the Monteregie region (210,000), Montreal (75,000), and Laval (55,000).

The utility said the outages were due to wind gusts and falling tree branches on the electricity network during the severe storm, and crews were in the field working to restore power.

"We are mobilizing all available crews to work tonight, issuing a massive call to ensure we can rely on restoring service by 5 AM Saturday," the statement read on its website.

"We are providing restoration times to the best of our knowledge at this point, but these times may vary significantly depending on the damage observed and the nature of the work required to restore power service."

A Hydro-Québec spokesperson, Louis-Olivier Batty, told CTV News that the vast majority of homes would regain power by Saturday morning, but some may wait until later that day or perhaps even until Sunday before power returns.

He added in an interview: "We understand this is not a pleasant situation for our customers. We thank them for their understanding and our crews will work hard tomorrow."

He noted that about 100 crews were in the field on Friday night and hundreds more would be deployed on Saturday morning.

The storm combined with a low-pressure system over the Great Lakes and moved through southern Ontario and Quebec, prompting Environment Canada to issue alerts and warnings from Cornwall, Ontario, to Quebec City regarding the risk of flash flooding.

The Lafontaine tunnel, which connects Montreal to the South Shore, was closed in both directions on Friday night, according to the Quebec transportation department.

The department reported several road closures in the Montreal area due to water accumulation on Friday evening, including the northbound Décarie Expressway near Royalmount Street.

In Pointe-Claire, lanes on Highway 20 westbound near Cartier Street were closed due to flooding.

Flooding also occurred on Highway 40 near exit 55 to Des Sources Street.

There were numerous delays and cancellations at Montreal Trudeau Airport on Friday due to the weather.

In the Saint-Laurent area of Montreal, the streets were filled with the sounds of generators and pumps as residents and businesses tried to prevent floodwaters from accumulating.

Alan Daigle, owner of the Benjamin Moore paint store at the corner of Côte-Vertu Street and Pollack Street, said: "Today, when we arrived here, the water was here and everywhere. The truck was parked, the car was parked, and the store was full of water. About eight inches."

Daigle stated that in 35 years of operation, the store had never flooded — until last month's record rainfall and again on Friday.

He added: "We just renovated the store... We were supposed to open on Monday, but I think we'll delay that again."

The Quebec transportation department said it prepared for this kind of weather by clearing debris from roads, but when it comes to this amount of rainfall, no equipment can keep up.

Transportation department spokesperson Louis-André Bertrand said: "We have powerful pumping systems, they are modern, and they are working at full capacity, but the problem is when we have exceptional amounts of rain like we had today and had in July, the storm sewer system cannot handle all this water."

The department urged all drivers to exercise caution while weather conditions were passing over the area.

In Saint-Laurent, many homes along Henry-Bourassa Street and Norman Street were flooded. Firefighters assisted exhausted homeowners in stacking sandbags and pumping out basements.

Harry Paparoutsis, whose basement was flooded, said: "The water kept rising. It just kept rising. And it overflowed."

Hydro-Québec advised homeowners to be cautious if floodwaters submerged their basements and to call 1-800-790-2424 to allow crews to cut power before going downstairs.

Heavy rains forced the cancellation of several events across Montreal, including some outdoor activities for the Montreal Pride Festival, such as Community Day in the Village and the 100 Percent Drag Party at the Olympic Park, which has been postponed to Saturday.

La Ronde amusement park, as well as Granby Zoo east of Montreal, also closed.

Events for the opening of the hot air balloon festival in Saint-Jean-sur-Richelieu, southeast of Montreal, have been postponed until Monday.

According to director Nacouset, floodwaters inundated the non-profit daytime shelter, Resilience Montreal.

Nicolas Minass, owner of a small shop in the Park Extension neighborhood of Montreal, said he was checking the store's basement for flooding before doing the same in his garage and his mother's basement.

Minass told the Canadian Press: "I have to go downstairs and check it from time to time because you never know when it’s going to happen. When it happens, it comes down and you can see that the drains aren’t absorbing the water fast enough."