Havana/Washington - Gustav strengthened to a dangerous category 4 hurricane late Saturday, as it made landfall in western Cuba and was on course to crash into the US Gulf Coast, three years after Hurricane Katrina.

Maximum sustained winds increased to 240 kilometres per hour, the Miami-based US National Hurricane Centre (NHC) said, and warned that Gustav "is an extremely dangerous category 4 hurricane on the Saffir- Simpson Hurricane Scale."

The scale ranks hurricanes from 1 to 5 in intensity, and NHC said Gustav could become a category 5 hurricane over the next 24 hours. A hurricane watch was issued for the northern Gulf Coast, from the state of Texas to the Alabama-Florida border, and the city of New Orleans.

By Saturday night, the eye of the hurricane was located about 915 kilometres southeast of the north-central Gulf of Mexico coast. "Gustav is forecast to remain a major hurricane through landfall along the northern Gulf Coast," NHC said.

In western Cuba, more than 60,000 people were evacuated, the Cuban News Agency reported. At least 10,000 Cubans moved from La Isla de Juventud, or the Isle of Youth, to the mainland, CNN said.

NHC has predicted "large and dangerous battering waves" along western Cuba and La Isla de Juventud, and heavy rains that will produce flash floods and mud slides.

More than 11.5 million Gulf Coast residents from Florida to southern Texas could be affected by Gustav, which would batter more than 176,100 square kilometres of coastline, the US Census Bureau said.

Thousands were streaming further inland from the US states of Mississippi, Louisiana and Alabama, where President George W Bush declared an emergency, allowing the federal government to coordinate disaster relief efforts.

"You need to be scared. You need to be concerned, and you need to get your butts moving out of New Orleans right now. This is the storm of the century," New Orleans Mayor Ray Nagin said.

While a mandatory evacuation was to start only at 8 am local time (1300 GMT) in New Orleans on Sunday, close to 10,000 people had already been moved out of the city on planes, trains and buses by Saturday night.

"We could see flooding even worse than we saw in Hurricane Katrina," Louisiana Governor Bobby Jindal told CNN. To cope with the crush of residents fleeing coastal cities, Jindal said he planned to open both sides of highways to outgoing traffic only early Sunday morning.

In 2005, Hurricane Katrina devastated New Orleans and much of the Gulf Coast in Louisiana and neighbouring Mississippi, leaving more than 1,800 people dead. Authorities have stressed that advances have been made in disaster response plans and in repairing levees since then.

Gustav has already claimed more than 80 lives in Haiti, the Dominican Republic and Jamaica.

Shipments of crude oil and natural gas from the Gulf of Mexico were hampered Saturday, after the largest US refining company - Valero Energy - cut production as Gustav advanced, Bloomberg financial news reported.

Most of the US oil and gas platforms and pipelines are located in the waters south of Louisiana and east of Texas. The nation's largest crude oil terminal, the Louisiana Offshore Oil Port, was also closed because of evacuations.

While Gustav will not reach St Paul, Minnesota - location of the Republican Party Convention that starts Monday - a potential landfall along the Gulf Coast will impact proceedings at the event that takes place more than 1,900 kilometres to the north of New Orleans.

Bush was severely criticized for attending political events after Hurricane Katrina wreaked havoc in New Orleans. He is to speak at the convention on Monday.