Rescue staff from the Municipal Emergency Management Agency investigate an empty car flooded during the passage of Hurricane Irma through the island in Fajardo, Puerto Rico. Picture: Alvin Baez/AP

Havana - Hurricane Irma menaced Cuba and the Bahamas on Friday as it drove toward Florida after lashing the Caribbean with devastatingly high winds, killing 21 people and leaving catastrophic destruction in its wake.

As Irma, one of the most powerful Atlantic storms in a century, bore down on Florida, Governor Rick Scott issued a stark warning for residents to get out if they were in evacuation zones.

"We are running out of time. If you are in an evacuation zone, you need to go now. This is a catastrophic storm like our state has never seen," Scott told reporters, adding the storm's effects would be felt from coast to coast.

US President Donald Trump said in a videotaped statement that Irma was "a storm of absolutely historic destructive potential," and called on people to heed recommendations from government officials and law enforcement.

Irma was about 270 miles (435 km) east of Caibarien on Cuba's central-north coast, and 405 miles (655 km) southeast of Miami, the National Hurricane Center (NHC) said in an advisory on Friday. Hurricane conditions were spreading westward over parts of Cuba and the central Bahamas.

The storm pummeled the Turks and Caicos Islands after saturating the northern edges of the Dominican Republic and Haiti.

The "extremely dangerous" storm was downgraded from a rare Category 5, the top of the scale of hurricane intensity, to a Category 4 early Friday but it was still carrying winds as strong as 150 miles per hour (240 km per hour), the NHC said.

Irma was forecast to bring dangerous storm surges of up to 20 feet (6 meters) to the southeastern and central Bahamas, and up to 10 feet (3 meters) on parts of Cuba's northern coast.

The storm was predicted to slam southern Florida on Sunday.

Cuba, where the Communist government has traditionally made rigorous preparations when the island is threatened by storms, was at a near standstill as Irma began to drive up the northern coast from east to west offshore.

Schools and most businesses were closed, hundreds of thousands of people were evacuated, and train, bus and domestic air services around the island were canceled. Airports were closing to international flights as conditions warranted.

Irma was forecast to move closer to land as it approached the center of Cuba later in the day and on Saturday, when it could seriously damage resorts on vulnerable keys. Tourists, and even the dolphins that entertain them, were evacuated. The storm was then predicted to veer north, sparing western Cuba and Havana.

In the Cuban fishing town of Caibarien, residents secured their roofs and moved belongings from low-lying coastal areas to houses higher up inland as the skies clouded over. Most said they were worried but well prepared.

Esteban Reyes, 65, was pushing his bicycle taxi laden with a mattress, iron and DVD player. "We are used to storms but I'm still a bit scared. But the government has taught us to be prepared and help one another," he said.

In the Bahamas, the government evacuated most people from the southern islands before the storm hit, with about 1 200 people airlifted to the capital, Nassau.

Irma was set to hit the United States two weeks after Hurricane Harvey struck Texas, killing about 60 people and causing property damage estimated at as much as $180 billion in Texas and Louisiana. Officials were preparing a massive response, the head of the Federal Emergency Management Agency said.

In several television interviews early Friday, Florida's governor pleaded with residents to leave areas designated for evacuation, although he acknowledged frustration with buying gas and handling bumper-to-bumper traffic on the roads.

"We're doing everything we can to get the fuel out," to gas stations, including police escorts, Scott told ABC's "Good Morning America" program.

Nearly one-third of all gas stations in Florida's metropolitan areas were out of gasoline, according to Gasbuddy.com, a retail fuel price tracking service.

Along with high winds, the NHC predicted dangerous storm surge flooding in Florida, with as much as 12 feet (3.5) meters in the state's south-west.

Miami-Dade Mayor Carlos Gimenez said authorities have asked about 660 000 residents to evacuate, adding this was the largest evacuation he could remember in the county.

US Senator Bill Nelson of Florida said the state was far more prepared now than in 1992, when Hurricane Andrew devastated Florida.

Supermarkets in Miami were full of shoppers picking up last-minute supplies and food, and long lines of cars wrapped around the few gas stations still open.

Kenneth Weipert, a stranded tourist from Scotland who was getting cash from an ATM at a boarded-up bank, said he had made multiple attempts to book a flight, with no luck.

"We have never been through anything like this before and we are quite worried about it," said Weipert. "We are in the hotel and the hotel is hurricane-proof, allegedly," he added.

In Palm Beach, the waterfront Mar-a-Lago estate owned by Trump was ordered evacuated, media reported. Trump also owns property on the French side of St. Martin, a French-Dutch island devastated by the storm.

A mandatory evacuation on Georgia's Atlantic coast was due to begin on Saturday, Governor Nathan Deal said. Virginia Governor Terry McAuliffe added his state on Friday to those under a state of emergency, saying it looked increasingly likely that Virginia could see "significant impacts" from Irma.

US stocks were little changed on Friday as investors assessed the financial impact of Harvey and tracked Irma. The three major Wall Street indexes were on track to end the week lower, with many economists forecasting that third-quarter gross domestic product will take a hit due to the hurricanes.

As it roared in from the east, Irma ravaged a series of small islands in the northeast Caribbean, including Barbuda, St. Martin and the British and US Virgin Islands, flattening homes and hospitals and ripping down trees.

A Reuters witness described the roof and walls of a solidly built house shaking hard as the storm rocked the island of Providenciales.

Even as they came to grips with the massive destruction, residents of the islands hit hardest by Irma faced the threat of another major storm, Hurricane Jose.

Jose, expected to reach the northeastern Caribbean on Saturday, was an extremely dangerous Category 4 storm, with winds of up to 150 mph (240 kph), the NHC said on Friday.

The death toll from Irma has risen as emergency services got access to remote areas.

French Interior Minister Gerard Collomb said on Friday nine people were killed, at least seven were missing, and 112 others were injured in St. Barthelemy and the French part of St. Martin.

France said it was deploying hundreds more police and other emergency personnel to the islands as it ramped up its response to the devastation in its overseas territories.

The Dutch government on Friday raised its estimate of casualties on its part of St. Martin to two dead and 43 wounded.

Four people died in the US Virgin islands, a government spokesman said, and a major hospital was badly damaged.

The eastern Caribbean island of Barbuda was reduced to "rubble," and one person died, Prime Minister Gaston Browne said. In the British overseas territory of Anguilla, another person was killed and the hospital and airport were damaged, emergency service officials said.

Three people were killed in Puerto Rico and a surfer was also reported killed in Barbados.

The storm passed just to the north of the island of Hispaniola, shared by the Dominican Republic and Haiti, damaging roofs and causing flooding and power outages as it approached the Haitian side. One man was reported missing after trying to cross a river in Haiti's Central Plateau region, and the government said some 10,000 people were in emergency shelters.