The few residents who have returned to flood-battered New Orleans have been ordered to leave as Hurricane Rita swells in the Gulf Coast.
Officials say New Orleans is not safe to reopen
The mayor of the hurricane-lashed city said the evacuation order would be enforced from later on Wednesday.
Ray Nagin said that if the hurricane, heading for Texas, shifted its path, it would not catch the city unprepared.
Officials say 500 buses are standing by to evacuate people and there are food and water supplies for half a million.
"We're a lot smarter this time around," Mr Nagin said.
He said he hoped everyone would be aware of the danger and leave without protest.
"We're all adults. We really don't want to take people out by gunpoint. We hope they see the threat ... and obey the law."
On the move
In early September, Hurricane Katrina breached the city's levees, sending water crashing into the low-lying city.
More than 800 people are now known to have died in the state of Louisiana, bringing the total death toll to over 1,000 in the region hit by Katrina.
Eighty per cent of the city was flooded, but the floodwater has now been pumped out, well ahead of schedule.
The army corps of engineers told the BBC the city is all but dry.
The BBC's Oliver Conway in New Orleans says a few puddles remain in road underpasses, but engineers say there are no mechanical means to get the city any drier.
Despite the latest warnings, some New Orleans residents remain sceptical.
"Like I say, you know, until the hurricane hits Canal Street, I ain't worried about it," James Pellet told the Associated Press.
Hurricane Rita is expected to make landfall in Texas on Saturday, where thousands of Louisiana residents who fled Katrina have been living in shelters.
As a mandatory evacuation order was announced they prepared to leave for a second time, heading to Arkansas and Tennessee by bus and plane.
"God, this day, right now, this place, with this foolishness going on, we need you," said Baptist Minister Johnny Jeremiah, the New York Times reported.
"Destination Unknown," said 71-year-old Catherine Womack as she boarded up her brick house in Galveston, Texas.
"I've never left before. I think because of Katrina, there is a lot of anxiety and concern. It is better to be safe than sorry."