Unrelenting rain is worsening a flood crisis in Central Canada that has already forced Quebec to call in military aid.

The Quebec government says the Canadian Forces have been enlisted to help battle the floodwaters in that province, where the storm has been most severe.

The troops are headed to Gatineau, Laval, Rigaud and the Mauricie region of Quebec. Another unit will be set up as a command post in Montreal. In total, between 350 and 400 military personnel have been deployed.

Hundreds abandon their homes

More than 120 Quebec communities have been hit by flooding and 857 people have been asked to leave their homes, according to Quebec authorities. More than 1,500 homes are flooded and 340 roads have been affected.

Environment Canada says a massive system is slowly drenching much of Ontario, Quebec and the Maritimes. Record precipitation levels have threatened to trigger widespread flooding in those areas.

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A man holds a dog Saturday as they navigate floodwaters by boat on Rue Saint-Louis in Gatineau. (Justin Tang/Canadian Press)

Rainfall advisories were lifted for the large urban areas of Montreal and Toronto early Saturday, but are still in place in eastern Ontario (including Kingston and Ottawa), parts of Quebec and most of New Brunswick. 

Rainfall amounts could range as high as 90 millimetres in Kingston, 130 millimetres from Sept-Îles to Natashquan, Que., and 100 millimetres in southwestern New Brunswick. 

A special weather statement says much of Nova Scotia could see close to 50 millimetres of rain.  

Bridge closure

In Montreal, a rehabilitation centre and a 76-unit condo have both been evacuated due to the swelling Rivière des Prairies.

Residents of the rehab centre have been taken to other health-care centres, where they'll stay for the next three weeks.

Île Mercier, an island of some 50 properties in Montreal, is completely underwater and has been under an evacuation order since Wednesday. 

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Residents drink beer while sitting in a flooded gazebo in Rigaud, Que. (Chris Wattie/Reuters)

Montreal Mayor Denis Coderre says the city may have to consider forcibly removing the 20 or so householders who have refused to leave, even as the only bridge connecting it to the rest of the city was shut down.

In Gatineau, Que., near Ottawa, around 400 people have been forced out of more than 200 homes as the Ottawa River rises.

Homeowner Jonathan Brennan told CBC News he'd been working since Monday to prevent his property from being flooded.

"Right now, I had to make a decision between pumping outside of my wall that I made or just take care of my basement," he said. "Because people didn't have a chance to prepare, there is old people around, there are abandoned houses ... If we had help from the army earlier, probably I wouldn't be like this right now.

"It's not that I failed, but I tried so hard. I don't know what to do anymore."

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State of emergency

On the other side of the river, the Ontario community of Clarence-Rockland declared a state of emergency in anticipation of continuing heavy rain.

The area's Chief Administrative Officer, Helen Collier, briefed residents Saturday, explaining that drinking water is safe but well water is not.

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A woman paddles a kayak past an abandoned car on a flooded residential street in Gatineau, Que. (Chris Wattie/Reuters)

Electricity was cut off on one road where a house was floating away, tethered only by power lines, the mayor said.

There have also been states of emergency declared in Gracefield, Pontiac and Oka.

Quebec's Minister of Public Security, Martin Coiteau, said that members of the Armed Forces have now joined municipal services, fire departments, police and civil security services in the relief effort.

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Floodwaters touch the bottom of a crucifix hanging from the rear-view mirror of a car abandoned on a residential street in Gatineau, Que. (Justin Tang/Canadian Press)

Quebec's Environment Minister, David Heurtel, said on Friday that the rain forecast is "beyond the worst scenarios that have occurred in the last 55 years."

Prime Minister Justin Trudeau promised the federal government was ready to do whatever it can to help people deal with the flooding and its cleanup.

A month's worth of rain

In New Brunswick, emergency officials are concerned about water levels and keeping a close eye on rivers and streams, including the St. John River.

In the southwestern part of the province, residents were warned that nearly a month's worth of rain was expected to fall in 24 hours.

CBC meteorologist Kalin Mitchell said the the rain would continue overnight Saturday and into Sunday morning. Some areas had already seen 50 mm by midday Saturday.

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Flooding is seen along Route 105 near Jemseg, N.B. (Philip Drost/CBC)

'I've never seen the lake come this close'

In their lakeshore home in Stoney Creek, Ont. on Friday, LeeAnn Lemay and Toni Burke peered out through the back window as the waves from Lake Ontario crashed over the retaining wall onto their small backyard.

Heavy rain has fuelled the high lake levels, sparking concerns about flooding and damage among some southern Ontario homeowners whose houses hug the shoreline of the lake. 

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Toni Burke stands in the backyard of her Stoney Creek, Ont., home located at the shore of Lake Ontario, as a wave crashes over her retaining wall. Burke says she has never seen the lake at such a high level. (Mark Gollom/CBC)

"I've never seen the lake come this close to the house," said Burke, who has lived in the area, located just outside of Hamilton, for over 40 years. "I have seen storms like this, but the lake wasn't so high.

"The water goes directly right across the street. So both sides of the street get it, it's not just the lakefront."

Next door to Lemay and Burke, the house built much closer to the shore took the full brunt of the waves, as the overflow from Lake Ontario crept into the front yard, flooding the whole area.

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The front yard of a Stoney Creek home located along Lake Ontario has been flooded. (Mark Gollom/CBC)

"Worst we've ever seen, absolute worst we've ever seen," said Lemay. "I'm concerned about our wall staying sturdy."

Lake Ontario's water levels are the highest they've been since 1993.

Bill Chornomaz, who works out of a home on the same street as Burke and Lemay, said water has already begun to leak inside.

"People are going to be experiencing flooding, no doubt," he said. "There will be basement flooding for sure."

Look at your insurance policy

When it comes to flooding, it would seem that many Canadians are unprepared. The University of Waterloo surveyed 2,300 homeowners who live in areas designated as high-risk flood areas. But nearly all (94 per cent) were unaware of that risk.

The study also found that those surveyed did not know recent government policy changes put the onus on homeowners to insure their homes specifically for flooding. 

"Canadians pay $600 million out of pocket for flood damage every year," Jason Thistlethwaite, an assistant professor at the School of Environment, Enterprise and Development at the University of Waterloo, said in a statement.

"With disaster-assistance costs expected to double over the next five years, homeowners can't afford to remain in the dark about their options and responsibilities."

'I tried so hard': Emotional Gatineau man on fight against floodwaters3:06

With files from CBC's Mark Gollom and The Canadian Press