Hurricane Irma is driving towards Florida after lashing the Caribbean with devastating winds and torrential rain, killing at least 19 people and leaving a swathe of catastrophic destruction.
Irma was about 724km southeast of Miami, Florida, early on Friday after saturating the northern coasts of the Dominican Republic and Haiti and pummelling the Turks and Caicos Islands.
The "extremely dangerous" hurricane was downgraded from a category five to a category four early on Friday but still packed winds as strong as 240km/h, the National Hurricane Center (NHC) said.
Irma hit the Bahamas on Friday, where it was forecast to bring 6m storm surges before moving to Cuba and then slamming into southern Florida on Sunday.
In Miami, hundreds lined up for bottled water and cars looped around city blocks to buy petrol on Thursday.
In Palm Beach, the waterfront Mar-a-Lago estate owned by US President Donald Trump was ordered evacuated, media reported.
Trump also owns property on the French side of St Martin, an island devastated by the storm.
A mandatory evacuation on Georgia's Atlantic coast was due to begin on Saturday, Governor Nathan Deal said.
The storm comes two weeks after Hurricane Harvey struck Texas, which claimed about 60 lives and caused as much as $US180 billion ($A222 billion) damage in Texas and Louisiana.
Irma ravaged small islands in the northeast Caribbean, including Barbuda, St Martin and the British and US Virgin Islands.
Throughout the islands, stunned locals tried to comprehend the devastation as they were getting ready for another major hurricane, Jose, a category three due to reach the northeastern Caribbean on Saturday.
The death toll from the storm has risen as emergency services got access to remote areas pummelled by heavy winds and rain.
French Interior Minister Gerard Collomb said on Friday that nine people were killed and at least seven were missing after the hurricane crashed into France's Caribbean islands of St Martin and St Barthelemy.
Four people died in the US Virgin islands, a government spokesman said, and a major hospital was badly damaged.
A man was reported missing after trying to cross a river in Cerca La Source in Haiti's Central Plateau region.
On Barbuda, one person died and the eastern Caribbean island was reduced "to rubble", Prime Minister Gaston Browne said.
In the British territory of Anguilla, a person was killed and the hospital and airport were damaged.
Three people were killed in Puerto Rico and about two-thirds of the population had lost electricity, Governor Ricardo Rossello said.
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, causing damage to roofs, flooding and power outages.
Cuba evacuated some of the 51,000 tourists visiting the island.
Irma is the strongest hurricane recorded in the Atlantic Ocean and one of the five most forceful storms to hit the Atlantic basin in 82 years, according to the NHC.
