Washington - Hurricane Gustav made landfall Monday near the town of Cocodrie in Louisiana state, the Miami-based US National Hurricane Centre (NHC) said.

Gustav was downgraded to a category two hurricane on the 1-to-5 Saffir-Simpson scale, with winds of 177 kilometres per hour, and was expected to generate a storm surge of 2-3 metres.

Forecasters said the eye of the hurricane could likely skim New Orleans, which is still recovering from 2005's Hurricane Katrina. But a hurricane warning remained in effect for New Orleans, and from east Texas to the Mississippi-Alabama border.

The hurricane would weaken as its centre moved inland over Louisiana, NHC said.

US President George W Bush, who got black marks for his administration's slow response to Katrina in 2005, cancelled his appearance at the Republican Party's national convention in St Paul, Minnesota on Monday, and travelled to Texas where rescue and recovery operations were headquartered.

Gustav, which at one point was an "extremely dangerous" category 4 hurricane, has already cut a path of destruction and killed 80 across the Caribbean before reaching its latest target area early Monday.

With memories of Hurricane Katrina - which killed 1,800 - still fresh, federal, state and local officials moved quickly to evacuate nearly 2 million residents along the coast from Alabama to Texas.

More than 7,000 people were evacuated by air out of Louisiana and about 337 critical care patients were transported by military aircraft, Dave Paulison of the Federal Emergency Management Agency (FEMA) said Monday.

An estimated 4,000 people were moved by train from New Orleans into Memphis, and there were about 45,000 people in shelters before the storm hit. Only about 10,000 people were still in the city, police said.

"We're waiting for the storm to pass. The National Guard, Coast Guard, Urban Search and Rescue teams are surrounding the city (New Orleans), ready to move back in as soon as the winds die down," Paulison told reporters.

Louisiana Governor Bobby Jindal estimated that 95 per cent of those threatened in the state had headed northwards to shelters, hotels and friends as far away as Tennessee and Oklahoma.

In St Paul, Minnesota, in the far-away northern tier of the country, the storm took a political, if not physical, toll.

Republicans meeting to nominate their presidential candidate, Senator John McCain, cancelled the political speeches planned for the convention opening on Monday.