BBC:-Hurricane Irma has caused widespread destruction across the Caribbean, reducing buildings to rubble and leaving at least 13 people dead.
The small island of Barbuda is said to be “barely habitable”. Officials warn that St Martin is almost destroyed, and the death toll is likely to rise.
Irma is a category five hurricane, the highest possible level.
It is currently north of the Dominican Republic, heading towards Turks and Caicos.
The low-lying Turks and Caicos islands, a British overseas territory, are said to be at risk of a storm surge, with the possibility of destructive waves up to 6m (20ft) higher than usual.
Virginia Clerveaux, director of the Turks and Caicos Department of Disaster Management and Emergencies, told the BBC that even inland areas could be inundated.
“We are now trying to remind them [the people of the islands] that this is a category 5, and in the history of the Turks and Caicos islands this is the largest storm we have ever been impacted or threatened by.
So there is a need to ensure that we have maximum preparations in place… we have been saying to persons to ensure that they are prepared, ensure they can shelter safely, they have sufficient food and drinking water for two to three days.”
Meanwhile, the head of the US emergency agency has said that Hurricane Irma will have a “truly devastating” impact when it hits southern coastal areas of the United States.
“The majority of people along the coast have never experienced a major hurricane like this,” Federal Emergency Management Agency (Fema) chief Brock Long told CNN.
The most powerful Atlantic storm in a decade, Irma has sustained wind speeds of 285km/h (180mph).
Hurricane Irma first struck the dual-island nation of Antigua and Barbuda. At least one death, of a child, was reported on Barbuda, where Prime Minister Gaston Browne said about 95% of the buildings had suffered some damage.
“It’s absolute devastation,” he said after flying over the island, home to some 1,600 people. “The island is literally under water. In fact, I’m of the view that, as it stands now, Barbuda is barely habitable.”
He told the BBC that 50% of the Barbuda population were now homeless and that it would cost $100m (£80m) to rebuild the island.
However, Antigua, with a population of 80,000, escaped major damage, with no loss of life, he said earlier.
St Martin, an island that comprises the French territory of Saint-Martin and the Dutch section Sint-Maarten, suffered terrible damage.
Officials have confirmed at least eight deaths in Saint-Martin and Saint Barthélemy, popularly known as St Barts.
“It’s an enormous catastrophe – 95% of the island is destroyed,” top local official Daniel Gibbs said of Saint-Martin.
Sint-Maarten’s airport, the third largest in the Caribbean, has been seriously damaged.
The Dutch defence ministry said: “The picture is of many uprooted trees, houses without roofs and pleasure boats on land.”
The Dutch navy has sent two ships from nearby Aruba and Curacao to assist locals but they have had trouble docking, according to media in the Netherlands.
Dutch Prime Minister Mark Rutte said: “The island is not reachable at this point because of the huge damage to the airport and the harbour.”
French Interior Minister Gerard Collomb said efforts were under way to get supplies to Saint-Martin and Saint Barthélemy.
“There is massive destruction. We’ll concentrate our first efforts so that in the next hours people can get access to food and drinking water,” he told reporters.
At least three people died in Puerto Rico, the governor’s office said.
The US territory’s capital, San Juan, saw waves of up to 30ft. More than 6,000 residents are in shelters, and many more are without power.
British overseas territories Anguilla and the British Virgin Islands were also caught in the extreme weather.
At least one death has been reported on Anguilla, a local official confirmed.
One Anguilla resident told the BBC the island looked as if it had been struck by a nuclear bomb, with roofs torn off many of the main buildings, including the hospital.
UK Foreign Secretary Boris Johnson said on Facebook that he had spoken with its chief minister.
“My thoughts are with all those affected and the UK is taking swift action to respond,” he said. “We have staff and a British naval ship ready to help those in need.”
Some residents complained that the UK response was inadequate.
UK Prime Minister Theresa May has arranged an emergency government meeting. She has spoken to French President Emmanuel Macron, pledging to work with him and the Dutch government to co-ordinate relief.
US President Donald Trump said he and his aides were monitoring Irma’s progress. “But it looks like it could be something that will be not good,” he told reporters at the White House. “Believe me, not good.”