Persistent, steady rains soaking swaths of Central and Eastern Canada that have already endured record precipitation levels threatened to trigger widespread flooding Friday and put residents and governments on high alert.

Environment Canada said a massive system was slowly drenching much of Ontario, Quebec and the Maritimes, triggering everything from contingency plans and flood warnings to states of emergency in dozens of municipalities.

In Montreal, Quebec Public Security Minister Martin Coiteux said Canadian Forces personnel have been enlisted to help cope with the crisis in the province.

"Considering what I've told you -- that the situation will deterioriate in the coming days, that the water levels in many Quebec regions are comparable to the largest floods we've experienced here ... I think additional resources are appropriate," Coiteux told a news conference.

"That's why I spoke today to Public Safety Minister Ralph Goodale and asked for reinforcements from the Canadian Forces."

Goodale said in a release Friday night that the Government Operations Centre has dedicated staff working to co-ordinate the federal response to the situation in Quebec.

"Citizens can rest assured that help will be provided as soon as possible," he said.

The province's environment minister, David Heurtel, said the rain forecast is for historic levels.

"It goes beyond the worst scenarios that have occurred in the last 55 years," he said.

It is not known how many soldiers will be involved or when they will arrive.

Senior climatologist David Phillips said the weather system, which stretches down as far as the southern United States, is stalled over the vast region due to high pressure systems elsewhere in the country.

The result, he said, is relentless rain falling on regions that have already endured double to triple the seasonal norms for rainfall over the past five weeks.

"The amount of moisture is significant," he said of the situation. "And, of course, when that falls on what you've already had, it makes it more of an impactful storm than it would be."

The problem is particularly acute in Quebec, where 132 communities had been affected by the floods as of Friday afternoon and some 700 people have been forced to abandon their homes.

For the residents of Ile Mercier, a small island in the middle of the Riviere des Prairies off the northern end of Montreal, rising water levels meant they could no longer cross their only bridge by car.

"The water is up to your knees on the bridge," said Nello Dicaprio, who has lived on the island for 11 years and decided to remain in the chalet he rents. "I've spoken to people who have crossed. They say the water is very cold and there is a current."

Dicaprio said he would wait out the situation and hoped the water levels would recede -- but he only had enough food for a few more days and there are no stores on the tiny island.

Chad Bouchard, who is taking care of his grandmother's house on the island, was less optimistic, with the water less than two metres away from the home as of Friday afternoon.

He said since authorities were no longer allowing cars on the bridge, he couldn't bring over any more sand bags to protect the house.

"We've been abandoned," he said. "But we still have control of the house. My uncle and our neighbour want to stay. It's our homes."

Jean-Francois Blais, who lives in central Quebec and had also been affected by the floods, called for more government help.

"It's desolation, it's really desolation," Blais told a news conference in Yamachiche, Que., alongside various politicians.

"We need help now and we will need help when these waters have left. There will be an enormous cleanup and we need help. That's obvious."

Assurances of assistance came quickly from Prime Minister Justin Trudeau during a scheduled stop in Montreal.

"Our thoughts are with the families and communities affected by the severe flooding that's going on throughout Quebec and indeed across the country," he said. "We stand ready and willing to give whatever help the federal government can to help people through this situation. And we will of course be there as the cleanup continues after the waters recede."

Meanwhile, residents of the Maritimes were being warned to expect a long stretch of heavy rain starting Saturday.

In particular, southwestern New Brunswick was expected to see the worst of it, with up to 100 millimetres of rain in the forecast.

The New Brunswick Emergency Measures Organization said the St John River basin is at capacity, which means flooding is likely.

"We're looking at persistent rain over several days," said Linda Libby, a meteorologist with Environment Canada in Charlottetown.

"The impacts are going to be greater because the ... conditions are already primed for flooding."

Western Nova Scotia and parts of Labrador can expect between 25 millimetres and 50 millimetres of rain over the weekend.

In Ontario, the eastern community of Clarence-Rockland had already declared a state of emergency in anticipation of heavy rainfalls expected to last through the weekend.

Warnings from Environment Canada forecast between 50 and 90 millimetres of rain for some communities across the southern and eastern parts of the province.

Phillips said that in places like Ottawa rain is expected to lead to flooding in the coming days.

The same holds true for Toronto, which announced a contingency plan to close the heavily travelled Don Valley Parkway expressway if water levels in the adjacent Don River rise too high. The city announced the road would remain open through the Friday afternoon rush hour, but noted a closure may still be necessary later on.

Ontario Premier Kathleen Wynne said emergency teams were on alert, and government officials were keeping a close eye on the situation province-wide.

"We are very aware of the situation around the province and monitoring it very, very closely," she said. "So just hope everyone stays safe."

Environment Canada has also posted severe thunderstorm watches for a large section of British Columbia's central and southern Interior, an area that is already contending with spring flooding.

An evacuation order was issued for Fintry Provincial Park on the northwest side of Okanagan Lake, while the River Forecast Centre said a flood watch was up for Mission Creek through East Kelowna and the Salmon River in Falkland, near Vernon.

Those areas were hit Thursday night by thunderstorms, as was Kamloops, where the deluge caused several already-swollen creeks to burst their banks.

Flooding also caused washouts of roads and bridges, as well as a rock slide near Highway 16 just east of the Alberta boundary.

With files from Giuseppe Valiante in Montreal.