The Mississippi River could crest late Monday in Memphis, where residents of more than 1,000 homes in low-lying areas have been urged to evacuate.

Down at the mouth of the river, in New Orleans, the Army Corps of Engineers has mobilized to limit the disaster as much as possible.

The complex system of levees and spillways constructed along America's biggest river held firm in Memphis against the pressure of rising floodwaters, which have crested at 14.63 meters (almost 48 feet) above flood stage.

The region still remembers the devastation caused in 1937 by cresting that reached 14.8 meters (48.7 feet).

The Army Corps of Engineers said it will open a spillway some 45 kilometers (28 miles) north of New Orleans to reduce the volume and speed of the crest.

The area where floodwaters will pour through the spillway can take more than 7 million liters (1.85 million gallons) of water per second, and will redirect the crest to the Gulf of Mexico through Lake Pontchartrain, north of New Orleans.

That should save a city that is mostly below sea level from the swollen current.

The National Weather Service said it does not expect rain in the Memphis region until Thursday, and that high temperatures can help contain the crest as it passes through the city.

Police in Memphis and the surrounding Shelby County have warned hundreds of people to get ready to evacuate their homes along the tributaries of the Mississippi since waters from the smaller rivers will likely be backed up, unable to flow into the great river because of its powerful, fast-moving crest.

On the other side of the river, authorities in Arkansas, a state where storms and flooding have taken 23 lives since mid-April, have declared a state of emergency in 63 of the 75 counties.

Arkansas Gov. Mike Beebe has requested federal government aid to deal with damages and the restoration of infrastructure, as well as to provide help for those left homeless.