Residents in the city of Memphis have been advised to prepare to leave their homes as the Mississippi River rises to record levels.
Elvis Presley's mansion Graceland is among the city's historic landmarks under threat.
A combination of heavy spring rains and melted snow have left the Mississippi at its highest level since the 1930s, the BBC reports.
The Mississippi River is expected to crest at 14.6 metres late on Monday or early on Tuesday in the Tennessee city.
Entire neighbourhoods in low-lying areas are partially under water. About 300 people have been put up in temporary shelters, but others are refusing to leave their homes.
The historic downtown area has been protected by a system of levees which officials believe should be able to withstand the peak flow on Monday night.
In places, the Mississippi is now six times its normal width and flooding is expected in several southern states over the coming days.