New Orleans is under curfew from sunset to dawn as Hurricane Gustav approaches.
More than a million people have fled Louisiana and highways out of New Orleans are full. Gustav could reach the coast as early as midday Monday.
New Orleans Mayor Ray Nagin said on Sunday that the first storm winds could hit New Orleans as early as daybreak on Monday and the hurricane could reach Category Four strength.
Gustav weakened to a Category Three storm (with winds of up to 125mph; 201km/h), but is expected to regain strength in the Gulf of Mexico before making landfall again.
A hurricane watch is in place from Texas along to the Alabama-Florida border.
It is three years since Hurricane Katrina devastated New Orleans. Three-quarters of the city was flooded on 29 August, 2005, when a storm surge breached its protective levees. More than 1,800 people died in coastal areas.
Republican candidate for the United States Presidency, John McCain, has suspended most of the first day of the party's convention in St. Paul, Minnesota, due to Gustav.
However, the convention will go on without President George Bush in attendence.
He plans to monitor the storm and evacuation operations in Texas.
Mr Bush also says he will not visit Louisiana in order to avoid interfering with evacuation and rescue operations.
Evacuations in Cuba
Gustav earlier hit Cuba after claiming at least 81 lives across the Dominican Republic, Haiti and Jamaica.
More than 250,000 were evacuated from western parts of mainland Cuba before the storm arrived.
Cuban television reports that the Isle of Youth was devastated.