Officials ordered the evacuation of one neighborhood and a nursing home late Thursday after authorities found cracks in an earthen levee built to protect the area from the threat of the rising Red River.

Residents were not in immediate danger, and floodwaters was not flowing over the levee, Mayor Dennis Walaker said Thursday night. The evacuation was being enforced as a precaution.

Officers were going door to door to the roughly 40 homes in the River Vili neighborhood and were evacuating Riverview Estates nursing home. The number of residents at the nursing home wasn't immediately clear.

Authorities across the river in Moorhead, Minn., also stepped up evacuations Thursday. They recommended that residents in the southwest corner of the city and in a northern area called Oakport Township leave.

Fargo residents have been scrambling in subfreezing temperatures to pile sandbags along the Red River. They spent much of Thursday preparing for a record crest of 41 feet - only to have forecasters add up to 2 feet to their estimate.

The first estimate sparked urgency among thousands of volunteers in Fargo, but the second sparked doubts about whether a 43-foot-high wall of water could be stopped. In Moorhead, City Manager Michael Redlinger said portions of his city's dike could not be easily raised to withstand a 42-foot crest.

"Now everything's up in the air," he said.

The old estimate was 41 feet by Saturday afternoon, and thousands of volunteers had labored throughout the day to raise the dikes around North Dakota's largest city to 43 feet. City and emergency officials had said they were confident the city would make it, but will now have to build higher.

The National Weather Service said in guidance issued late Thursday afternoon that the Red was expected to crest between 41 and 42 feet, but could reach 43 feet. It said water levels could remain high for up to a week - a lengthy test of on-the-fly flood control.

"Record flows upstream of Fargo have produced unprecedented conditions" on the river, which "is expected to behave in ways never previously observed," the weather service said.

Tim Corwin, 55, whose south Fargo home was sheltered by sandbags to 43 feet, said he wasn't giving up but was pessimistic after hearing the new potential crest.

"I've lived here 40 years and over a 30-minute span I've reached a point where I'm preparing to evacuate and expect never to sleep in my house again," he said.

Even before Thursday's revised estimate, official briefings in Fargo had lost the jokes and quips that had broken the tension earlier in the week. Instead, Thursday's meeting opened with a prayer.

"We need all the help we can get," Walaker said.

The city of 92,000 unveiled a contingency evacuation plan Thursday afternoon, but at least four nursing homes already had begun moving residents by then.

"A few of them said they didn't want to go. I said I'm going where the crowd goes," said 98-year-old Margaret "Dolly" Beaucage, who clasped rosary beads as she waited to leave Elim Care Center.

"I'm a swimmer," she said, smiling, "but not that good a swimmer."

The sandbag-making operation at the Fargodome churned as furiously as ever, sending fresh bags out to an estimated 6,000 volunteers who endured temperatures below 20 degrees in the race to sandbag.

"I was skeptical as far as volunteers coming out today, but they're like mailmen," said Leon Schlafmann, Fargo's emergency management director. "They come out rain, sleet or shine."

Gov. John Hoeven, heading into a planning meeting in Fargo, urged residents not to let down. "We know they're tired, but we need to hang in there and continue the work," he said.

Hoeven was calling for 500 more National Guard members to join 900 already part of the effort.

Walaker, the mayor, said he was shocked by the new forecast.

"Is this a wakeup call? People can't take many more wakeup calls," he said. But Walaker also said the forecast didn't seem to match what he had seen in the Red's tributaries earlier in the day.

"This is the worst-case scenario," he said. "Right now, I'm going to stick with 41," he said.

As in Fargo, sandbagging was under way in Moorhead, a city of about 35,000 where some homes in a low-lying northern township had already flooded. The city was setting up a shelter at its high school for displaced residents and those who heeded the call for voluntary evacuation.

Moorhead Mayor Mark Voxland told WDAY-TV that the city would just have to raise its protection another foot.

"The problem is we don't have that much time. Every day is a day closer to crest and now we're looking at 36 hours to cresting - we don't know if we have time to add another foot to all of our dikes."

As the struggle continued in Fargo, the threat in the state capital of Bismarck was receding. A day after explosives were used to attack an ice jam on the Missouri River south of the city of 59,000, the river had fallen by 2 1/2 feet. At least 1,700 people had been evacuated from low-lying areas of town before the river began to fall.

Crews were rescuing stranded residents in rural areas south of Fargo. Pat Connor of the Cass County sheriff's department said 70 people had been rescued by Thursday evening, and that the number would probably go up.

In Fargo, the southern parts of the city, mostly residential areas, were seen as most vulnerable, and the city was building contingency dikes behind the main dike in some areas. The river was a bit over 39 feet Thursday evening. The Red hit 39.57 feet in 1997, and the record is 40.1 feet in 1897.

Dick Bailly, 64, choked up as he looked out over his backyard dike at the river.

"It was demoralizing this morning," Bailly said, his eyes welling. "We got a lot of work to do. People have the will to respond, but you can only fight nature so much, and sometimes nature wins."

On a sandbag line behind another house near the river, 65-year-old Will Wright, a veteran of Fargo floods, helped stack bags as water began to seep through his homemade dike. Like others, he said he was confident the dike would hold - for a while.

"The big concern I have is the river crest staying three to five days and it testing the integrity of these sandbags," Wright said.

In Moorhead, both entrances to the Crystal Creek development were flooded, leaving Deb and Scott Greelis thinking about how they and their kids - ages 6, 2 and 6 months - could get out if things get much worse.

"We are pretty much stuck in here," Deb Greelis said. But she said they could haul the kids in a sled to a nearby highway on higher ground if they need to evacuate.

On the Canadian side of the Red River, in Manitoba, ice-clogged culverts, ice jams and the rising river also threatened residents. At least 40 homes were evacuated in communities north of Winnipeg and several dozen houses were flooded as water spilled onto the flat landscape.

"We're in for probably the worst two weeks that this community has ever seen in its entire existence," said St. Clements Mayor Steve Strang.

The region's emergency services coordinator, Paul Guyader, said water levels in the area were dropping but residents are not letting their guard down: The Red River crest threatening North Dakota isn't expected to arrive in Manitoba for another week.