Faced with the threat of a major flood, the mayor of Valley City called Tuesday for the evacuation of sick and elderly residents, as well as those living in low-lying areas, so that emergency crews could focus on trying to hold back the swollen Sheyenne River.

Mayor Mary Lee Nielson asked affected residents to leave their homes by Wednesday evening, saying it would help keep emergency routes free of traffic.

"We may need to get people in and out of there in a hurry," she said.

Nielson said the evacuation order is voluntary but "strongly recommended." She said it would affect about 1,450 homes — "not quite half the city" of nearly 7,000 people.

About 450 National Guard members have been called in to help, the mayor said. Crews have had to repair at least three dike leaks in recent days, but Nielson said there were no reports of problems with the dikes overnight Monday.

"It was a blessing," she said.

The Sheyenne River rose Monday above the 20-foot Valley City record set in April 1882. At 6 a.m. Tuesday, it was up to 20.58 feet, headed to a crest of around 22 feet in the next couple of days, according to the National Weather Service.

The river empties into the Red River, which is expected to reach a second flood crest of its own near Fargo this week.

The Red River crested at Fargo and neighboring Moorhead, Minn., late last month just short of 41 feet, after volunteers filled thousands of sandbags to raise levees above that mark. The river's second crest there is projected to reach 37 feet, which is lower than earlier forecasts.

The National Weather Service has posted flood warnings for much of North Dakota. Roads are flooded throughout the state, and state Transportation Department Director Francis Ziegler said some highways will have to be completely rebuilt. A 100-mile stretch of Interstate 94 between Bismarck and Jamestown was reopened Tuesday after an overnight closure because of flooding, but officials imposed a 5 mph speed limit.

In Walsh County, in northeastern North Dakota, Sheriff Lauren Wild said a man missing since his pickup was swept away near the town of Park River early Sunday was presumed drowned. Two other people in the truck swam to safety.