|Heavy rains have caused widespread flooding in Missouri, Illinois, Kentucky, Tennessee, and Arkansas [AFP]
Residents of Memphis are being told to leave their homes for higher ground as the Mississippi river edged toward the city, threatening to bring more flooding to parts of an area already soaked.
Officials went door-to-door on Sunday, warning about 240 people to vacate the premises before the river reaches its expected peak on Tuesday.
In all, residents in more than 1,300 homes have been told to leave, and some 370 people are now living in shelters.
Memphis residents have been abandoning low-lying homes for days as the dangerously surging river threatened to reach 14.63 metres, just shy of a 14.84-metre record of a devastating 1937 flood.
Record river levels, some dating as far back as the 1920s, have already been broken in some areas.
Heavy rains and snowmelt have been blamed for the flooding.
The situation was further exacerbated by continuous rain in Memphis on Saturday.
"Reality has set in, so now we're getting more calls,'' Alvin Pearson, assistant manager of operations for the Memphis bus service, said.
In the small town of Hickman, Kentucky, officials and volunteers spent nearly two weeks piling sandbags on top of each other to shore up the 27.4km levee.
About 75 residents were told to flee town, but by Saturday, the levee had held, and officials boasted that only a few houses appeared to be damaged and no one had been injured or killed.
"We have held back the Mississippi river and that's a feat,'' said one emergency management director, Hugh Caldwell. "We didn't beat it, but it didn't beat us."
Billions of dollars have been spent on levees and other flood defences built over the years, and engineers say it is unlikely any major metropolitan areas will be inundated as the water pushes downstream over the next week or two.
However, farms, small towns and even some urban areas could see extensive flooding.
Since the Great Mississippi Flood of 1927, a disaster that killed hundreds, the US congress has made protecting the cities on the lower Mississippi a priority.
The Army Corps of Engineers has spent $13bn to fortify cities with floodwalls and carve out overflow basins and ponds a departure from the "levees-only" strategy that led to the 1927 disaster.
More than four million people live in 63 counties and parishes adjacent to the Mississippi and Atchafalaya rivers from Cairo, Illinois, south to the Gulf of Mexico, census figures show.