San Francisco/Fargo, North Dakota  - Residents of North Dakota's largest metropolitan area were evacuating Friday as the Red River roared to its highest ever level and a crack appeared on a crucial sandbag dike.

The US Army Corps of Engineers was building a secondary dike behind the compromised barrier that sprang a leak as the river, which runs from Canada through Minnesota and North Dakota, rose to record- breaking 12.22 metres.

The Red River is expected to crest at 12.8 metres on Saturday, topping many of the dikes designed to protect the Fargo-Moorhead metropolitan area and its population of 343,000.

An estimated 6,000 volunteers had worked throughout the icy cold night filling sandbags to reinforce the dikes, even as many homes were already flooded in other parts of the north-central state along the Canadian border, the local newspaper the Forum reported on its website.

"We do not want to give up yet. We want to go down swinging if we go down," Fargo Mayor Dennis Walaker said, even as authorities ordered mandatory evacuations for numerous neighbourhoods.

Many of the evacuation orders were issued in the middle of the night as alarms blared throughout the area and residents had to leave on foot as temporary backup dikes blocked the roads.

In aerial flooding views broadcast on television, single homes with snow-covered roofs looked like small islands as flood waters rose against sandbag walls. People moved about in boats.

Ice chunks floated in the flood waters and snow covered the nearby hills, emphasizing how cold the temperatures were in the far northern region. The flooding followed a huge snow blizzard late last week in the region.

Elsewhere there was better news as water receded in the state capital, Bismarck, where 1,700 people had been evacuated, the Bismarck Tribune reported. The problem there was compounded by an ice flow on the Missouri River that officials used explosives to help clear on Wednesday.

President Barack Obama has declared much of the state a disaster area to free up aid money from Washington.

Elsewhere in the United States, spring weather spurred tornadoes.

In the Gulf Coast state of Mississippi, 20 people were injured, a church was destroyed and 60 homes were damaged by a twister in the town of Magee, broadcaster CNN reported. Forecasters were warning of more possible tornadoes Friday. (dpa)