Open this photo in gallery Roger Brouillard carries his belongings down a flooded street in Ste-Marthe-sur-le-Lac, Que., on Sunday. Ryan Remiorz/The Canadian Press

The slow-building floods of Eastern Canada have turned into a full-blown emergency, with the rupture of a dike near Montreal triggering a sudden inundation that forced 6,500 people to flee to higher ground on the weekend.

About one-third of the residents of Sainte-Marthe-sur-le-Lac grabbed what they could and bolted for safety Saturday night and Sunday morning, often leaving with only the clothes on their backs. No one was hurt or missing after the water rushed into the town on the bank of Lac des Deux Montagnes across from western Montreal. Quebec Premier François Legault described the successful evacuation as “a near miracle” as he visited the scene.

Sainte-Marthe-sur-le-Lac flood levels, as of Saturday Sainte-Marthe- sur-le-Lac Laval Montreal 0 7 KM 0 750 Flood levels m Flooding Flooded vegetation 640 Sainte-Marthe-sur-le-Lac CHEMIN D’OKA Lake of Two Mountains MURAT YUKSELIR / THE GLOBE AND MAIL, SOURCE: TILEZEN; OPENSTREETMAP CONTRIBUTORS; GOVERNMENT OF CANADA Sainte-Marthe-sur-le-Lac flood levels, as of Saturday Sainte-Marthe- sur-le-Lac Laval Montreal 0 7 KM Flood levels Flooding 640 Flooded vegetation Sainte-Marthe-sur-le-Lac CHEMIN D’OKA 0 750 m Lake of Two Mountains MURAT YUKSELIR / THE GLOBE AND MAIL, SOURCE: TILEZEN; OPENSTREETMAP CONTRIBUTORS; GOVERNMENT OF CANADA Sainte-Marthe-sur-le-Lac flood levels, as of Saturday Sainte-Marthe- sur-le-Lac Laval Montreal 0 7 KM Flood levels Flooding 640 Flooded vegetation Sainte-Marthe-sur-le-Lac CHEMIN D’OKA 0 750 m Lake of Two Mountains Bizard Island MURAT YUKSELIR / THE GLOBE AND MAIL, SOURCE: TILEZEN; OPENSTREETMAP CONTRIBUTORS; GOVERNMENT OF CANADA

Floodwaters are not set to crest until Tuesday and vital infrastructure will remain under pressure well into May as water slowly recedes.

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In the most serious flood zone stretching from Ottawa to Montreal along the Ottawa River system, the situation seemed to have been stabilizing. Then the dike broke just after dinner Saturday, driving the number of flooded houses and evacuees past the record levels of 2017.

After the water rushed in, Jason Meunier hopped into the front-end loader he was using to reinforce a friend’s dike. He used it to push abandoned cars out of the way and to ferry 16 people from their houses in the early hours Sunday morning. “It was really unbelievable,” he said. “The water was up to people’s arms and the current was too strong to walk in.”

Francis Labbé heard that the dike had broken when he arrived home and checked his buzzing phone. He thought it was a prank. Within minutes he saw water shooting from manholes on his street. He took a few minutes to move valuables from his finished basement to the main floor before the police knocked on his door.

Here’s what you need to know about flooding in Quebec, Ontario and New Brunswick

Maryse Kahlé-Lépine returned to her childhood home by skiff Sunday to rescue her two cats, Petit Gars and Moustache, that the family had left behind. Her mother, Anne-Marie, died last December, Ms. Kahlé-Lépine said. “We’ve had enough loss. We lost our mother. We might be losing the house. We weren’t going to lose them too,” she said.

Sureté du Québec officers went door to door to confirm people were out. “Everyone is safe,” Sergeant Daniel Thibaudeau said. Town Mayor Sonia Paulus, who had to abandon her own flooded home, said the small remaining rise should not add much to the damage. “Honestly, it can’t get much worse now. The lake is in the town,” she said. Crews were building new temporary dikes to try to isolate the worst-flooded area and allow the rest to be drained.

The broken dike was built about 40 years ago and had undergone inspection and upgrading just last year after successfully protecting the town in 2017, the mayor said. It was too early to know the cause of the breach, she said.

Provincial authorities reported that across Quebec, as of Sunday evening, 6,424 homes are flooded and 9,522 people have left for higher ground. The toll has surpassed the record-breaking Quebec floods of 2017, which cost provincial coffers $376-million, not including insurance claims or amounts people spent out-of-pocket.

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“These are big numbers and the coming hours are critical,” Quebec Public Security Minister Geneviève Guilbault said. She added: “There is no rain forecast until at least Wednesday. It should stabilize conditions and allow everyone to catch their breath.”

So far one woman has died in Eastern Canada’s spring flooding after the road she was driving on in Western Quebec was washed away April 20.

The province and Hydro-Québec are still closely monitoring a dam at Bell Falls about 120 kilometres northwest of Montreal where the Rouge River spilled around the facility. Officials remained confident it would hold. Mr. Labbé, who fled his home in Sainte-Marthe Saturday, was part of a Hydro-Québec team monitoring the situation. “We got less water than we could have,” Mr. Labbé said of the dam. “We got a break.”

In Ontario, water was still rising on the Muskoka River and expected to exceed 2013 levels that saw more than 1,000 permanent residences and 1,000 seasonal homes flooded. Bracebridge is one of several communities north of Toronto, including Huntsville and Minden Hills, that have declared emergencies.

In the Ottawa-Gatineau region, 5,500 volunteers bolstered by 5,500 military personnel set sandbags to save homes in outlying towns on the Ontario side. The Chaudière Bridge from Ottawa to Gatineau was closed to pedestrians and vehicles due to high water levels. In Gatineau, the water flooded 461 homes, most of them in the historic heart of the town.

In New Brunswick where about 1,000 people were evacuated from 240 flooded homes, the water was receding. But officials in that province say there’s a long way to go before the response can become a recovery effort. Communities along the Saint John River from Fredericton to Saint John remained above flood stage.

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Prime Minister Justin Trudeau didn’t close the door Sunday on using federal dollars to help relocate communities facing the recurring threat of severe flooding.

Since the Liberals took office in late 2015, the government has approved almost $1.27-billion in funding for 41 projects deemed “disaster mitigation,” according to federal figures. The numbers show that only a handful of projects have started and many will take years to complete.

Mr. Trudeau suggested, the federal government needed to make sure future infrastructure spending hits the “right” projects.

“Once we secure the situation through this spring flooding season, we will have to have significant reflections and conversations on how we move forward,” he said.

With reports from Barrie McKenna in Ottawa, Danielle Edwards in Toronto and The Canadian Press