An ice jam clogging the Missouri River north of Bismarck ruptured Wednesday, sending more water flowing toward the city where flooding already had led to some evacuations.

The National Weather Service issued a flash flood warning for a three-county area after the ice jam broke.

"What you have now is water rushing from the ice jam that is to the north. We could see a rapid rise of 1 or 2 feet in water levels," said weather service meteorologist Joshua Scheck.

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Officials had already called for more volunteers to help with sandbagging as record amounts of water poured into the Missouri River from its tributaries.

National Guard members flew over the river Wednesday morning to assess the flooding conditions and the possibility of dropping explosives to break up another ice jam, south of the city, that was backing up water in the metropolitan area.

Some of the ice is in 3-foot-thick chunks, as big as a small car, and it will be tough to get them moving, assistant state Water Commission engineer Todd Sando said Wednesday.

The call for volunteers Wednesday in Bismarck was made after residents of low-lying subdivisions in Bismarck and Mandan were told to leave their homes as access roads flooded.

Fox Island residents Jane and Michael Pole didn't need much prodding to evacuate. "We just grabbed a bag, threw some stuff in and left," Jane Pole said.

Some 200 miles east of Bismarck, officials also called for more sandbagging volunteers in Fargo, and its cross-river neighbor, Moorhead, Minn., where the Red River was projected to crest at 39 to 41 feet Friday evening. It had risen to 34 feet by early Wednesday. The record for Fargo is 39.6 feet set in the 1997 flood.

Officials said the flood threat intensified when the region was struck Tuesday by the blizzard that had shut down wide areas of the northern Plains.

President Barack Obama declared North Dakota a federal disaster area, which means the federal government will pay 75 percent of state and local government costs for the flood fight.

Sand supplies briefly ran out in Fargo early Wednesday because icy roads made travel difficult for a Minnesota supplier. City officials quickly found a local supplier and said they were 95 percent done with the effort to raise dikes to 42 feet. Engineers were being sent out to make sure the dikes were sound.

Snow was still falling Wednesday in the Red River Valley region, with several inches on the ground, and people were advised not to travel. The continuing bad weather forced Grand Forks to cancel two busloads of volunteers who planned to head upstream to Fargo.

More sandbagging was planned in part of Grand Forks, the city hardest hit by the 1997 Red River flood. An elaborate dike system was built after that disaster. The Red had risen to nearly 42 feet in Grand Forks on Wednesday morning with a crest of 50 to 53 feet projected for Monday or Tuesday, compared with the record of 54.4 feet set in 1997.

The Army Corps of Engineers on Tuesday cut water releases for the first time ever from the Garrison Dam on the Missouri River north of Bismarck to ease flooding. No water will be released from the dam until flooding eases in Bismarck, spokesman Paul Johnston said.

A reduction in the water releases takes about two days to reach the city, he said.

Cutting releases from Garrison will cut power generation at the dam and force the Western Area Power Administration to buy electricity on the open market to meet obligations to its customers, Johnston said.

The Bismarck area got 8 inches of snow from the blizzard, with wind gusting to more than 45 mph, the National Weather Service said Wednesday morning. Light snow continued falling Wednesday morning, with a temperature of 19 degrees, the weather service said.

The blizzard had blocked hundreds of miles of highways in Montana, Wyoming, South Dakota, North Dakota and Nebraska. The southwestern North Dakota town of Marmarth reported 22.5 inches of snow and up to 2.5 feet of snow fell in South Dakota's rugged Black Hills.