The US heartland, already coping with record floodwaters, may have to wait for some relief.

Flooding that has caused more than a billion dollars in damage is likely to last into next week, as rain and melted snow flow into Kansas, Missouri and Mississippi, the National Weather Service said.

Surging waters have damaged hundreds of homes and been blamed for at least three deaths, two in Nebraska and one in Iowa. The flooding has harmed agriculture, inundating tens of thousands of acres, threatening stockpiled grain and killing livestock.

The flooding was so intense because rain fell upon a snow-covered region that was unable to absorb much of it, The New York Times reported.

"A lot of it stems from the fall flooding in September and October," Mindy Beerends, a senior meteorologist at the Des Moines office of the National Weather Service, told the Times. "The soil was saturated in the fall."

She said the moisture stayed in the ground all winter while snow accumulated, and when warm air and rain arrived, the snow melted.

"The higher-than-average precipitation, combined with warm temperatures, snowmelt and the frozen ground was a perfect storm for flooding," she said.

The icy surface made the water spread the way liquid would across a tiled floor, was how the Times described it.

"The ground was like concrete," said Kevin Low, a hydrologist at the service's Missouri Basin River Forecast Center, told the paper.

Nebraska Governor Pete Ricketts put flood damage at more than $1.3 billion, including $439 million in infrastructure, $85 million in private homes and businesses, $440 million in crops and $400 million in livestock, weather.com reported.

On Wednesday, Minnesota Governor Tim Walz sent National Guard troops and a Chinook helicopter to Nebraska to help with the emergency response.

A levee breach Wednesday morning caused evacuations of the town of Craig, Missouri, home to about 240 people, KMBC.com reported.

"The town will be fully inundated within a few hours," said the town's Twitter account. "If you haven't moved, don't try now to get out of town. Don't drive through running water."

In Iowa, farmer Jeff Jorgenson estimated that in Fremont County more than a million bushels of corn and nearly a half-million bushels of soybeans were lost in flooded grain bins. For the 28 farmers in the area, the grain loss was estimated at $7 million.

"The economy in agriculture is not very good right now. It will end some of these folks' farming, family legacies, family farms," Jorgenson said. "There will be farmers that will be dealing with so much of a negative they won't be able to tolerate it."

In Glenwood, Iowa, Mayor Ron Kohn said farms west of the city are likely finished for the year.

"That's all going to be gone until next year, I'm sure," he told the Des Moines Register. "Rice is about all they could grow out there now."

There is also concern that floodwaters could contain untreated sewage and harmful chemicals found in fertilizers.

"It is vital that everyone working near floodwaters realizes the risks that exist," Randall Williams, Missouri Department of Health and Senior Services director, told the Kansas City Star on Monday. "Just as driving in moving or standing water is dangerous, wading in floodwaters or exposure while recovering from a flood can pose health risks."

Vice-President Mike Pence flew over the flood zone on Tuesday with the governors of Iowa and Nebraska, who have asked President Donald Trump to declare a national emergency in both states.

Amtrak said Tuesday that it was temporarily halting its Missouri River Runner Service between Kansas City and St. Louis. It said freight traffic was being diverted to tracks Amtrak uses, and buses were transporting passengers instead.

More than a dozen levees have breached in Missouri, Iowa and Nebraska, according to the US Army Corps of Engineers, which handed out hundreds of thousands of sandbags to help with the flood fight.

Water also was lapping at the edge of the tiny community of Fortescue, Missouri and another levee was at risk of breaching in Forest City, Missouri.

The Associated Press and Reuters contributed to this story.