New Orleans is braced for the arrival of Hurricane Isaac exactly seven years after the city was battered by Hurricane Katrina.
Isaac hit coastal areas of Louisiana with winds of up to 80mph and is heading towards the city.
Thousands of people have evacuated the area and New Orleans airport has shut.
Power cuts have been reported across low-lying parts of Louisiana and Mississippi, affecting more than 200,000 homes and business as president Barack Obama declared an emergency in both states.
New Orleans Mayor Mitch Landrieu said a 26ft high levee gate that now protects areas of the city that were badly flooded in 2005 was closed yesterday.
"We will not have a Katrina-like event," he said, adding there will still be parts of the city that will likely be flooded.
"Do not let this storm lull you into complacency," he said. "People may be getting bored. It's better to be bored than to get hurt."
Isaac has killed at least 24 people in Haiti and the Dominican Republic while causing significant flooding and damage in the Caribbean.
The US National Hurricane Centre warned that a possible combined "storm surge" and high tide would cause flooding in coastal areas along the Gulf Coast.
Water would potentially reach 6-12ft (1.8-3.7m) above ground in south-west Louisiana and Mississippi, 4-8ft in Alabama and 3-6ft in south-central Louisiana.
Isaac is also threatening heavy rainfall of as much as 20 inches and could spark possible tornadoes along the northern Gulf Coast.