Hurricane Gustav weakened slightly to a Category 2 storm as it headed towards New Orleans today, the US National Hurricane Centre said.
The city resembled a ghost town this morning after its mayor warned "the storm of the century" was coming and it was "time to be scared".
Torrential downpours swept across the US Gulf coast three years after New Orleans was devastated by Hurricane Katrina. Forecasters warned the eye of the hurricane and its 110mph winds would hit Louisiana at around 5pm UK time.
An estimated two million people have been evacuated in the state, Federal Emergency Management Agency (Fema) deputy director Harvey Johnson said.
The main threat to New Orleans appeared to be flooding, with an "extremely dangerous" storm surge of 10ft to 14ft in tidal levels on some areas of the coast.
But despite the mass evacuation in recent days, many residents were resolutely staying on.
Aileen Bennett, 43, originally from London, lives in one of the areas set to be worst hit.
From her home in Lafayette, about 110 miles west of New Orleans, she said earlier: "I am actually standing outside and it is blissfully quiet and beautiful.
"It has not been what we were expecting but we are prepared."
The latest forecast from the US-based National Hurricane Centre (NHC) said the worst of the storms would sweep through Louisiana, west of New Orleans.
The NHC's latest update said reports indicated that "maximum sustained winds have decreased to near 110mph, with higher gusts".
It went on: "No significant change in strength is likely before landfall with weakening expected to begin after Gustav moves inland later today.
"Hurricane force winds extend outward up to 70 miles from the centre and tropical storm force winds extend outwards up to 230 miles."
President George Bush and Vice President Dick Cheney skipped the Republican Party's national convention after presidential hopeful John McCain suspended the majority of proceedings because of mounting concerns about Gustav.
Mr Bush, who was severely criticised for his administration's poor response to the Katrina disaster, warned America yesterday of the "dangerous" threat posed by the storm.
He urged residents on the US Gulf coast to heed local warnings and added: "Know that the American people stand with you and we will face this emergency together."
He was widely attacked in the wake of Katrina, which killed more than 1,800 people in US coastal areas, for a slow, apparently casual, approach to the disaster and the relief effort.
Today, he was travelling to Texas to meet emergency workers and evacuees.
Democratic presidential nominee Barack Obama also stepped into the crisis and offered to tap his huge network of donors and volunteers to help any victims of Gustav.
"I think we can get tons of volunteers to travel down there if it becomes necessary," Mr Obama said.
Gustav has already left a trail of death and destruction in its wake, killing 94 people across the Caribbean.
New Orleans mayor Ray Nagin imposed a dawn-to-dusk curfew from sunset last night as Gustav approached and said the storm would be "big and ugly".
Looting, one of the major problems in the wake of Katrina three years ago, would not be tolerated, Mr Nagin said.
Another Briton defying the warnings was James Lewis, 38, who left Putney, south west London, to run a pub in New Orleans.
He said he was defying the order to prevent "what happened to my pub when Katrina rolled in - looting and mindless destruction".
The Crown & Anchor is located on the west bank of the Mississippi River, which is being evacuated.
Yesterday, Mr Lewis, 38, said: "The general consensus here is (the mayor) is covering his back after the colossal muck-up over Katrina."
The US authorities' actions will be closely scrutinised after what was widely seen as a series of catastrophic failures in its slow and inadequate response to Katrina.
After Katrina hit land on August 29 2005, three-quarters of the city was flooded after the storm surge breached its protective levees.