As hurricane Gustav approached and buses transported the last New Orleans residents to safety on Sunday, Mayor Ray Nagin warned that anyone staying behind to loot homes would face the full force of the law.

The city is under a mandatory evacuation order and Nagin has also ordered a dusk-to-dawn curfew to prevent robberies.

"Looters will go directly to jail. You will not get a pass this time," Mayor Ray Nagin told reporters on Sunday. "You will not have a temporary stay in the city. You will go directly to the Big House."

The evacuation order became mandatory at 8 a.m. local time on Sunday for the more vulnerable west bank of the Mississippi River, and starts at noon on the east bank.

Police and Louisiana National Guard troops remain behind to patrol evacuated neighbourhoods. "We will have unprecedented security," Nagin promised.

Three years ago, hurricane Katrina swamped the city's flood defences. Much of New Orleans is below sea level. More than 1,800 people died and property damage ran into the billions of dollars. Social chaos followed, with widespread looting and other crime occurring in Katrina's immediate aftermath.

Many neighbourhoods still aren't rebuilt, and there are questions whether the city's levees and other defences can withstand another major hurricane.

The U.S. National Hurricane Center in Miami has issued a hurricane warning for an area from Cameron, La. eastward about 800 kilometres to the Alabama-Florida border, meaning hurricane conditions are expected within the next 24 hours.

New Orleans and Lake Ponchartrain are included in that zone. But a hurricane watch also extends east of Cameron into Texas.

"Preparations to protect life and property should be rushed to completion," the center advised.

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New Orleans Mayor Ray Nagin, center holds a news conference at City Hall in New Orleans, on Saturday, Aug. 30, 2008. (AP / Bill Haber)

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Derek Webb and Amber Nightengale, of Washington, march down Bourbon Street with their luggage as they try to escape Hurricane Gustav in New Orleans on Sunday, Aug. 31, 2008. (AP Photo/Eric Gay)

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Harry Janoswky prays before Mass at the St. Louis Cathedral in New Orleans' French Quarter Sunday, Aug. 31, 2008 in New Orleans. (AP Photo/Ron Heflin)

Alabama also issued mandatory evacuation orders for some of its coastal areas. U.S. President George Bush also urged all Gulf Coast residents to evacuate, warning the flooding risk was considerable.

Gustav is currently rated as a Category 3 hurricane with sustained winds of 185 kilometres per hour, but forecasters believe it will regain strength and become a Category 4 storm as it passes over the warm waters of the Gulf of Mexico today.

At 5 p.m. ET, it was located about 350 kilometres south of the Mississippi River's mouth, moving northwest at 28 kilometres per hour.

Nagin said his officials hope the hurricane, if it hits New Orleans, will move out quickly. The city's pumps can remove 2.5 centimetres of rainfall per hour for the first two hours, then capacity falls by about half, he said.

Gustav could drop up to 30 centimetres of rain, with 50 centimetres possible in some areas, forecasters say.

Cuba, the Gulf

Gustav was at Category 4 strength when it passed over Cuba with winds of 220 kilometres per hour, leaving homes and roads damaged or destroyed in its wake. However, while there were many injuries, no deaths were reported.

Gustav made landfall at Los Palacios in the heart of the country's tobacco region.

The hurricane has left 81 people dead so far, mainly by triggering floods and landslides in Haiti, the Dominican Republic and Jamaica.

In advance of the storm, oil and gas companies started shutting down their operations in the Gulf of Mexico. The U.S. Minerals Management Service said Saturday that more than three-quarters of all oil production and 40 per cent of gulf natural gas facilities were shut down.

The Gulf represents about one-quarter of U.S. oil production. Analysts say a prolonged shutdown would drive prices up for gasoline and other petroleum products.

Meanwhile, Tropical Storm Hanna is approaching the Turks and Caicos Islands and is expected to land either late Sunday or on Monday. It is expected hit the Bahamas and possibly Cuba in the coming days.

Hanna has sustained winds of 95 km/h. The hurricane center said it could lead to dangerous rip currents off some parts of the southeastern U.S. coastline.

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