Hundreds of volunteers built temporary dikes out of sandbags and clay amid a light drizzle of rain Tuesday as the flat prairie state of North Dakota braced for record spring flooding.

Army trucks filled with sandbags drove down a normally quiet residential street lining the Red River in Fargo where fresh volunteers poured out of buses to join a line of people tossing bags onto an ever-increasing dike.

"People are starting to realize how serious this situation is," said Kyle Lunke, a student at North Dakota State University.

"Everybody counts in these times. We'd like to think they'd be there for us."

The entire state was under a major flood warning as an unusually heavy snowpack began to melt on top of saturated land that has not yet fully thawed.

Floodwaters have already shut down a number of roads and bridges across North Dakota, where the governor has called in the national guard to help with flood protection and rescue efforts.

Several people caught in the rising waters were evacuated by air after roads became impassable and dozens more were forced to abandon their homes.

A heavy blizzard expected to dump six to nine inches of snow was forecast to move eastward across the state on Tuesday, further complicating flood preparations.

The neighboring state of Minnesota was also under threat as the mighty Red River, which borders the two midwestern states, began to overtop its banks as it flowed slowly northwards to Canada.

The extreme flatness of the Red River Valley means the floods will go wide, move slowly and take days or even weeks to recede, said Pat Slattery of the National Weather Service.

"You will have an extremely wide river," said Slattery, who said a stretch of waterway that now measures 100 yards wide "might turn into a mile to a mile-and-a-half."

"It's very hard to get this stuff to run off," he added. "Your soil up there is totally saturated."

It usually takes about two weeks for a flood crest to flow the 393 miles (633 kilometers) from the southern end of North Dakota to the Canadian border because of the flatness of the land.

Any rain or snowfall in the coming weeks will raise flood levels even further, warned Slattery.

The region was the site of devastating flooding in 1997, which caused more than two billion dollars in damage and forced tens of thousands of people from their homes after about 2,200 square miles (3,540 square kilometers) of land were swamped.

Since then, flood protections have been reinforced and officials say they are determined not to lose another home or business to the river.

"I don't think any homes are doomed to be lost," said Karena Lunday, the city of Fargo's communication manager.

Volunteers have poured into the city of 100,000 people to help with sandbagging efforts, and had filled a million by Tuesday morning.

A million more will be needed to protect the city from a flood forecast to crest at a near-record 40 feet on Friday, Lunday said.

Several miles of dikes need to be built and reinforced to protect against the river that runs through the east side of town.

"Everyone is so determined to get the job done," Lundy told AFP. "With so many volunteers stepping up to help I think we'll make it."

Jennifer Paulsrud fell asleep to the sound of trucks dropping off sandbags outside her Fargo home, which survived the 1997 flood thanks to a barrier built in the backyard.

That plywood barrier has been elevated this time around with the help of sandbags dropped off by volunteers.

"I woke up in the morning and there were sandbags everywhere," said Paulsrud as she handed out sandwiches and pizza to volunteers.

"It's a deja vu kind of thing ... I didn't think it would happen again."

Paulsrud has faith that the heavy flood wall will protect her green one-story home and says she has never considered leaving the lovely tree-lined street on the river's edge.

"This will always be our home," she said.