Officials have ordered the evacuation of one neighbourhood in Fargo, North Dakota after crack in a earthen levee built around the area was found.
Authorities say the move is a precaution and the 40 homes in the neighbourhood are not in immediate danger.
A local nursing home was also evacuated.
Fargo is at high alert as forecasters now say the Red River could crest as high as a record 13 metres.
The situation is equally grave in Manitoba, where more than 800 could be forced from their homes as rising flood waters on the Red River imperil towns and cities in the south of the province.
Officials warned that over the next three weeks, many communities will suffer through "prolonged agony" as the spring thaw accelerates flooding.
Near Winnipeg, flood forecaster Alf Warkentin said that ice jams could cause overland flooding, despite new flood channels built in the wake of record water levels in 1997.
The torrent of flood waters has been slowed recently by cold weather, but officials said Thursday that the cool temperatures have only put off the inevitable deluge.
South of the border, Fargo was bracing for serious flooding Thursday night as residents worked around the clock to fill 500,000 sandbags, said CTV's Jill Macyshon.
"And they'll need more, because we're hearing tonight that Red River is rising again," she said, noting that the city is in a race against time to reinforce dikes.
Macyshon added that the river in some areas is clogged with chunks of ice the size of cars.
"You're never safe when there's a flood on. No one really knows what to expect of what to predict."
She added that the worst case scenario could see an evacuation of the entire city of Fargo, which has a population of around 92,000.
Unpredictable river waters
Back in Canada, the mayor of a Manitoba town warned residents that the worst was not over, even though blocks of ice that have put the area under a major flood alert have begun to break apart.
"The ice jam has broken up but only to resettle in another area and the process starts all over again," said St. Clements Mayor Steve Strang. "Mother Nature will decide when she's going to crack this baby loose."
The water began to subside Thursday after crews worked through the night chopping at blocks of ice, hoping to relieve the ice jam.
Nonetheless, Strang said there are about 100 frozen culverts that are blocking melting snow from flowing away.
It's like working "a double-sided sore," he said.
Nonetheless, the province's emergency measures co-ordinator, Paul Guyader, said the crews' efforts were paying off as water levels in the area are beginning to drop. He also noted that crews were working to pump water from flooded areas and had put out piles of sandbags.
The Manitoba government has also sent 2,700 metres of tube diking to emergency areas.
However, Guyader warned residents that the worst was far from over.
"We're not going to get a reprieve at all," he said.
Meanwhile, about 100 residents were evacuated from their homes Thursday afternoon on the Roseau River First Nation as flood waters continued to rise.
"We're ready to get everyone out who the band council deems necessary," Curtis Smith, executive director of the Manitoba Association of Native Firefighters, told CTV News.
"We already have volunteers down there registering people to make sure no one gets left behind."
In St. Andrews, at least 12 homes were flooded and 40 more are still at risk. Residents there told CTV Winnipeg the water seems higher than it was during 1997's "flood of the century."
St. Andrews, St. Clements, and East and West St. Paul are all under a state emergency. Dozens of homes in the region have already been evacuated due to flooding after the ice jam, located near Lockport, backed up the river's waters.
East St. Paul residents have not been forced to evacuate as of Thursday afternoon, but the municipality's chief administrative officer is advising people to be prepared.
While the breakup of the ice jam dropped water levels by two feet, the ice jam "has just moved on up, not very far down the road," Jerome Mauws told CTV Newsnet from East St. Paul.
"With additional ice coming down the river, it's starting to jam again. And we're concerned the levels are going to start to rise again."
'Worst two weeks'
Next week, major flooding is expected along the Red River, which flows northward from North Dakota into Manitoba, from spring runoff.
"We're in for probably the worst two weeks that this community has ever seen in its entire existence," said Strang in an interview with The Canadian Press.
On Saturday, officials say the Red River will crest at 12.5 metres.
Pat Zavoral, an administrator with the city of Fargo, said 1997's "flood of the century" was only 12.1 metres.
"We're dispensing these sandbags out into these neighbourhoods where we have 45 kilometres of dikes that we have to reinforce to a higher level for the crest that's going to happen on Saturday," Zavoral told CTV on Thursday.
He said officials originally thought they'd only need 350,000 sandbags to fight back the waters.
"Three days ago we upped it from 1 million to 3.5 million sandbags and I think we're going to surpass that," Zavoral said.
Still, Zavoral said he was confident that the dikes would be able to hold off the water.
Forecasters predicted flooding would be particularly bad this year because of heavy rain last fall which saturated the soil before freezing over during the colder months. Ice jams caused problems all the way down the Red River to North Dakota.
Residents living along the North Dakota part of the Red River are working frantically to build dikes high enough to hold back the water.
Meanwhile, residents in North Dakota are working around the clock as the Red River rises into what Mayor Dennis Walaker described as "uncharted territory."
To the west, residents along parts of the Missouri River have also been told to evacuate because of rising water levels.
U.S. President Barack Obama has declared North Dakota a federal disaster.
As a federal disaster area, the federal government will pay for 75 per cent of state and local government costs to deal with the flooding.
With files from The Canadian Press and The Associated Press
