The US National Hurricane Centre has said Hurricane Gustav is now the same strength as Hurricane Katrina, which struck New Orleans three years ago.
It also warned that Gustav could become a Category 5 Storm before crossing Cuba.
The Mayor of New Orleans says he will order a compulsory evacuation of the city tomorrow morning if Hurricane Gustav stays on its current course.
More than 70 people have already died in the Caribbean as a result of the Category 4 storm, which is expected to reach Cuba in the coming hours, before crossing the Gulf of Mexico.
Mass evacuations are underway on the island and the southern United States as Gustav is due to make landfall in the coming hours.
Officials said the hurricane gathered strength as it moved over the warm waters of the Caribbean with wind speeds in excess of 185km/h.
The storm is still on track to strike the heavy concentration of US oil and natural gas platforms off Louisiana.
The most likely track has it going ashore west of New Orleans on Tuesday.
US emergency officials warned that Gustav was expected to be accompanied by a five-to-nine metre storm surge along the Gulf Coast, and said four states in its potential path were expected to begin large-scale evacuations today.
Louisiana authorities warned residents to prepare to evacuate and laid on transportation for those who do not have cars.
US President George W Bush has declared a state of emergency in both Louisiana and Mississippi.
