The Mississippi River broke through a segment of an earthen levee in Missouri on Friday, with officials warning the leak will "ultimately inundate" part of an eastern town in the state.

The National Weather Service said the Pin Oak Levee at Winfield, about 72 kilometres northwest of St. Louis, burst around 5:30 a.m. local time and threatened about 100 homes in the community of about 720 residents. Authorities said they believe holes burrowed by muskrats likely caused the levee to break.

"It's so disappointing," said Linda Wilmesherr as she peered through binoculars at water pouring through a gap that appeared to be nine metres wide. "With all the guns in this county, couldn't we kill a muskrat?"

Within hours of the breach, authorities rushed to assemble a makeshift sandbag levee more than one metre tall to protect homes in the floodwaters' path. The surrounding rural area is also expected to flood.

"We're not quitting — the army doesn't quit," said National Guard Col. Michele Melton, who was co-ordinating the sandbagging effort. "That's why we're here — to try and save these people."

Residents of the community said the siren sounded and sheriff's deputies went door-to-door to get everyone out of the homes, yelling, "The levee broke! Get out!"

Winfield resident Debbie Halcomb, 52, was sleeping in a bed elevated on milk crates to protect it from potential floodwaters when the siren sounded.

"Oh my God. I was hoping it would hold, but it didn't," Halcomb said. "I think we probably lost it on this last bunch of rain."

The U.S. Midwest has been reeling from record flooding in recent weeks, leaving thousands homeless and billions of dollars in damages from crop losses and property destruction.

With files from the Associated Press