The southern US city of Memphis is coping with flood levels not seen since the 1930s, which have forced people from at least 1,300 homes.
The Mississippi River was expected to crest at 48ft (14.6m) late on Monday or early on Tuesday in the Tennessee city.
The authorities have evacuated low-lying neighbourhoods, but officials say they are confident flood control systems will prevent further harm.
The flooding has been caused by melting snow and heavy rains.
Rising water levels
Army engineers say it is unlikely that the levee system in Memphis will give way, but have admitted that the water has been rising faster than expected.
The authorities have also warned residents to look out for snakes and rats which could seek shelter on higher ground.
Officials downstream in Louisiana have begun evacuating prisoners from one of the state’s toughest prisons – the Louisiana State Penitentiary in Angola – and opened floodgates to relieve pressure on levees outside New Orleans.
Police in Memphis have gone door-to-door to 1,300 homes during the past several days to warn people about the rising water levels.
More than 300 people were staying in shelters on Monday, and police increased their presence in evacuated areas to prevent looting.
“I imagine that my trailer, if it’s not covered, it’s close,” Aurelio Flores, an unemployed construction worker, told the Associated Press news agency.
On Monday evening, Tennessee Governor Bill Haslam said even though the river was approaching its crest, the water would not recede in some neighbourhoods for at least two weeks.
“It’s not going to get a lot better for a while,” Mr Haslam said.
The National Weather Service said the Mississippi River would probably crest later on Monday evening or early on Tuesday.
Forecasters had previously said the crest could come as late as Wednesday.
The record river height of 48.7ft was set in February 1937 during one of the worst Mississippi floods in US history.
Officials said they were confident levees along the river would hold back the water and that the authorities had 20,000 sand bags in reserve in case of a breach.
Col Vernie Reichling Jr of the Army Corps of Engineers, which manages the Mississippi River flood control system, told reporters: “There should be no concern for any levees to fail.”
In downtown Memphis, the river had swollen to three miles (4.8km) wide from its typical width of half a mile, the Memphis Commercial Appeal newspaper reported.
