Gustav strengthened to a dangerous category 4 hurricane late Saturday, as it ripped through Cuba and was on course to crash into the US Gulf Coast, three years after Hurricane Katrina, REPORTED DPA. 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 Alabama-Florida border, and the city of New Orleans. More than 11.5 million Gulf Coast residents from Florida to southern Texas could be affected by Gustav, the US Census Bureau said. It also calculated that the hurricane would impact more than 176,100 square kilometres of coastline. In western Cuba, more than 60,000 people were evacuated, the Cuban News Agency reported. Thousands were streaming inward from the US states of Mississippi and Louisiana. On Saturday, President George W Bush declared an emergency in Mississippi and Alabama, allowing the federal government to coordinate disaster relief efforts. He had declared an emergency in Louisiana on Friday. Hundreds of people lined up at bus and train stations to get out of New Orleans, whose mayor Ray Nagin said, "I am strongly, strongly encouraging everyone in this city to evacuate. Start the process now. Don't wait." Nagin said officials evacuated 1,200 people by bus and 1,500 by train. Another 20,000 residents had registered to be evacuated from various points across the city, which is still haunted by Hurricane Katrina. If Gustav stayed on course overnight, New Orleans would start a mandatory evacuation at 8 am local time on Sunday (1300 GMT), Nagin told a news conference. "We could see flooding even worse than we saw in Hurricane Katrina," Louisiana Governor Bobby Jindal told CNN. 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 at least 70 lives in Haiti, eight in the Dominican Republic and four in Jamaica. The National Aeronautics and Space Administration (NASA) was to close its Michoud Assembly Facility in New Orleans at midnight on Saturday because of the anticipated landfall of Gustav. Michoud provides vital support to NASA's exploration and discovery missions. 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, Republican officials told CNN. 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.