President George W Bush is heading to Texas to oversee the planned response to Hurricane Gustav, which is expected to make landfall near New Orleans at 5pm UK time.
Mr Bush hopes to demonstrate that he has learnt the lessons of Hurricane Katrina, which dealt a blow to the president's reputation.
Although New Orleans is in Louisiana, many of the refugees from the city are seeking shelter in neighbouring Texas, which is also being used as a staging point for emergency response efforts.
Gustav has been downgraded to a Category Two hurricane, but the US National Hurricane Center said it remained an "extremely serious" threat.
Mr Bush, a former Texas governor, had been due to speak today at the Republican convention in St Pauls Minnesota, which also lies in the Hurricane's path.
But with the storm preparing to strike, all today's keynote speeches have been cancelled.
Gustav is likely to do most damage to the low-lying Cajun areas west of New Orleans, where levees are in a poor state of repair and the land has long suffered coastal erosion.
"This could be our Katrina," said a Louisiana state senator, Reggie Dupre.
The evacuation is the largest in state history, with thousands more leaving threatened areas in Mississippi, Alabama and southeast Texas.
Bobby Jindal, Louisiana's governor, issued one last plea to the roughly 100,000 people still left on the coast, telling them: "If you've not evacuated, please do so. There are still a few hours left."
In New Orleans, a dawn to dusk curfew was enforced by police and National Guardsmen roaring through the deserted streets in Humvee vehicles.
Gustav, which has already killed at least 94 people in the Caribbean, appeared to have claimed the lives of another three following unconfirmed reports that three patients in critical care had died during the evacuation of Louisiana hospitals.
Mr Jindal said he expected the state's levees, which gave way with such devastating consequences during Hurricane Katrina three years ago, would just be able to withstand the storm.
Referring to weather and engineering experts, he said: "If they are 100 per cent accurate, they are saying the levees will barely hold or barely be overtopped."
Gustav is currently expected to pass to the west of New Orleans. It has also been moving more quickly and is losing strength, both factors that have reassured observers that it may prove less damaging than previously feared.
But Mr Jindal warned: If the storm "deviates its intensity or path slightly, we could still see significant surge flooding. It's too early, premature to think we're beyond that danger."
Wind speeds this morning registered around 115 mph and Gustav is expected to remain a Category 3 storm when it makes landfall.
New Orleans is likely to be on the "dirty" side of the storm, subjecting it to heavy rainfall and possible tornadoes.
But the 25ft storm surge that caused Katrina to breach the levees currently appears unlikely to be repeated.
The US National Huricane Centre forecast a storm surge of no more than six feet in New Orleans as a result of Gustav.
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