Gustav is expected to become an "extremely dangerous" Category 5 storm, the most powerful hurricane possible, as it roars through Cuba and heads toward the U.S. Gulf coast.

Category 5 storms have sustained winds of more than 249 kilometres per hour. Winds of that speed will create a storm surge of more than five metres, rip off most roofs and completely destroy mobile homes, according to the U.S. National Hurricane Center in Miami.

At 11 p.m ET on Saturday, Gustav had maximum sustained winds of 220 kilometres per hour with higher gusts. The centre of the storm was located 145 km west of Havana, Cuba.

Gustav's winds have lashed Cuba's Isla de Juventud, where 87,000 people live.

"The rain is not so intense, but there is a lot, a lot of wind," Isabel Alarcon, who lives on the small island in the city of Nueva Gerona, told The Associated Press. "The officials, they have told us the wind will be bad first but then the rain could cause flooding into the night."

Gustav is moving in a northwest direction at 24 km/h, and is expected to continue in that direction for the next few days. It's centre is expected to pass over Cuba by Sunday morning.

The National Hurricane Centre says Gustav "could reach Category five intensity" in the next 24 hours and is "extremely dangerous."

Cuba is rushing to evacuate 240,000 people from the storm's path.

Residents and emergency officials in the "Gulf of Mexico and northern Gulf Coast should closely monitor the progress of Gustav," the advisory said. "A hurricane watch could be issued for portions of the Northern Gulf Coast later today."

Gustav has left at least 78 people dead so far in the Caribbean. It struck the Cayman Islands on Friday, its winds knocking down trees and power lines.

However, Hemant Balgobin, disaster manager for the Red Cross in the British territory, said, "Things weren't really as bad as they could have been."

On Friday, Gustav left four dead as it passed over Jamaica, and left at least 4,000 people homeless. At least 59 people died in Haiti and another eight in the Dominican Republic.

The storm is expected to cross the heart of Cuba's cigar country today. Cuban state television announced that effective today, all buses and trains to and from Havana have been suspended until further notice.

Gustav will head into the Gulf of Mexico on Sunday. It could lead to the temporary shutdown of 80 per cent of the Gulf of Mexico's oil and gas production. Hundreds of oil workers have already been evacuated from offshore platforms.

Retail gasoline prices are already rising in response.

CIBC World Markets predicted Friday that Canadians could see prices of up to $1.75 per litre.

Meanwhile, Tropical Storm Hanna should reach the Bahamas by early this coming week. It is currently recording sustained winds of 80 kilometres per hour.

With files from The Associated Press