Vast stretches of the Midwest remained threatened by what the National Weather Service described late Monday as "major to historic" flooding, even as officials and residents were still grappling with a recent deluge that left three people dead in Iowa and Nebraska.

The flooding occurred after downpours and snowmelt swelled rivers and creeks across the region last week.

Flood warnings and advisories remained in effect across the Plains, the Mississippi Valley, and parts of the Ohio Valley region on Monday, the weather agency said.

Speaking to reporters Monday, Iowa Gov. Kim Reynolds called the floods "catastrophic" and "unbelievable."

"It was heart-wrenching to see the breadth of the flood," she said, recalling a flight over the Missouri River earlier.

Forty-two of Iowa's counties had declared emergencies, she said. Two-thirds of the town of Hamburg, just east of the Missouri river, was "lost," she said.

Buffy Chaney, who moved there a few years ago — and whose home remained underwater Monday — told NBC affiliate WOWT that the experience was "heartbreaking."

"Just watching rescue boats go down, I mean, it's speechless," Chaney said. "Devastating. Heartbreaking."

In Nebraska, where White House Press Secretary Sarah Sanders said Vice President Mike Pence would travel on Tuesday, that state's emergency management agency tallied the flood's financial impact at more than $265 million, according to WOWT.

In Douglas County, which includes Omaha, 200 children and adults had been rescued since Friday, WOWT reported.

At a horse stable there, it wasn't clear if 18 animals would escape the floodwaters alive, according to NBC affiliate KSNB.

The owners of Winnail Stable had to flee on Saturday before the horses could be evacuated, the station reported.

When volunteers returned with food, they found one donkey dead and the horses alive, though standing in chest-deep water, the station reported.

"We're going to make it," said an airboat pilot working with the stable, according to the station. "I guarantee we'll get there."