Red River may have peaked in North Dakota
The National Weather Service had earlier said the river could crest on Sunday afternoon as high as 13.1 metres, the same height as the levees.
That assessment was later revised, with the National Weather Service reporting that it's possible the river reached a high point of 12.44 metres around midnight.
Forecasters said levels can still fluctuate by as much as 30 centimetres, depending on the movement of ice floes.
"The best news we can take from this is the river has crested," Fargo Mayor Dennis Walaker said. "But diligence is going to have to be required for at least eight more days and hopefully things will continue to drop."
Officials have cautioned that the city of Fargo still wasn't out of the woods because the river was expected to stay more than six metres above flood stage for several days, testing the strength and integrity of dikes.
Freezing temperatures overnight slowed the rise of the river, but despite the encouraging news, state officials intensified their efforts to fend off the high water.
The number of National Guard troops on flood-watch duty in North Dakota increased from 1,700 to 1,850 on Saturday. The troops will help secure earthen levees or seal cracks that develop.
Officials were also bringing in 300 large bags that hold a tonne of sand, material that could be dropped into breaks in the levees.
Volunteers fill millions of sandbags
No major levee breaches or other issues were reported during the night.
Thousands of volunteers have filled about three million sandbags over the past week, local officials said. On Friday, the river rose to 12.28 metres, breaking a record set 112 years ago. There was some localized leaking overnight, and in one of the neighbourhoods at greatest risk in Fargo, people were still reporting sewage water seeping into basements.
Across the river in Moorhead, Minn., officials were forced to evacuate one neighbourhood Friday night because the roads had become impassable.
Thousands of people who live along the river in both Minnesota and North Dakota have fled to higher ground because of flooding or the threat of rising water.
Elderly, people with children asked to move to higher ground
Fargo Deputy Mayor Tim Mahoney said only vulnerable adults, such as the elderly, or people with children were being asked to move.
He said the temperature plunged to –10 C overnight.
In his weekly radio and internet address, President Barack Obama said he would " continue to monitor the situation carefully" and that federal officials "will do what must be done to help."
Obama said the U.S. Army Corps of Engineers, the Coast Guard, the Defence Department, the National Guard and the Health and Human Services Department, as well as the American Red Cross, were involved.
With files from the Associated Press