Residents of this tiny community cleared out Wednesday as water spilled over a nearby dam and began eroding it, while officials in the larger town of Valley City to the north urged thousands of people to evacuate from their homes because of a flooding threat that could persist for weeks.

National Guard soldiers in helicopters were dropping one-ton sandbags to help shore up the Clausen Springs Dam a few miles from Kathryn, a town of about 55 residents that could become inundated if the dam breaks. Julie Nelson, a spokeswoman for the Barnes County emergency management team, said the dam was being eroded by water spilling over it.

Residents fled to relatives' homes or a Red Cross shelter after officials went door to door Wednesday morning telling them to get out.

Fire Chief Paul Fisher was on Kathryn's Main Street monitoring the flow of water through three culverts. If they were to break, he said, "I'll make one more sweep through town and get out of here."

There was no evidence of major flooding by early afternoon, although some homes had water in their yards and signs of seepage in basements.

Kathryn is about 17 miles south of Valley City, which is battling record high water on the Sheyenne River. The Clausen Springs Dam is on a tributary of the river.

In Valley City, the elderly, disabled and people living in low-lying areas had been urged to evacuate by 6 p.m. Wednesday to make sure emergency routes were kept open.

The National Guard had a Blackhawk helicopter and some high-wheeled vehicles ready in case troops are asked to assist with evacuations, said Capt. Dan Murphy. He said there were no problems with Valley City's dikes during the night.

Murphy said the U.S. Army Corps of Engineers was closely monitoring Baldhill Dam, upstream from Valley City on the Sheyenne, trying to calculate how much water the dam can hold back in its reservoir and how much can be released without adding too much to the river.

The river rose Monday above the 20-foot Valley City record set in April 1882. It reached 20.6 feet Tuesday but fell to 20.33 feet by noon Wednesday, the National Weather Service said.

The flood risk to Valley City could last a month, said Greg Wiche, director of the U.S. Geological Survey's Water Science Center in Bismarck.

Valley City Mayor Mary Lee Nielson said Tuesday that her town's evacuation order was voluntary but "strongly recommended." She said it affects about 1,450 homes — "not quite half the city" of nearly 7,000 people.

Fran Aune and her stepdaughter, Deb Wacha, were moving Aune's belongings out of her duplex Wednesday. Aune and her husband, Andrew, planned to set up a camper on a higher part of Valley City and wait out the floodwaters.

"It's scary," she said. "We've been praying a lot."

The Sheyenne empties into the Red River, which is expected to reach a second flood crest of its own near Fargo this week. The Red 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. Projections of the river's second crest have been lowered to around 35.5 feet to 36 feet.

Roads across North Dakota were flooded. Amtrak suspended service Tuesday between Minot and St. Paul, Minn., because of track flooding east of Minot.