The second maximum-strength storm to rage over the Caribbean this month has killed at least one person in Guadeloupe and is barrelling towards Puerto Rico after devastating the small island nation of Dominica.
On St John Island, which was also battered by Hurricane Irma two weeks ago, locals reported seeing trees dramatically swaying in swirling winds, with rain pouring "sideways."
Judi Buckley, former senator for St Croix Island, traveled to St John from her South Carolina home to help with the Irma relief effort - only to get caught up in Maria.
"Rain is coming through sideways and the trees are swaying," she told AFP.
"We have become the Irma relief hub and our brothers and sisters across the pond can't afford for us to be crippled," she said, referring to those on St Croix.
On Tuesday, Maria, a rare Category 5 storm at the top end of the five-step Saffir-Simpson scale, churned in the eastern Caribbean about 175km southeast of St Croix in the US Virgin Islands, US forecasters said.
It was carrying maximum sustained winds of 260km/h, the US National Hurricane Center (NHC) said, describing Maria as "potentially catastrophic".
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Dominica braces for Hurricane Maria
"Maria is forecast to remain an extremely dangerous Category 4 or 5 hurricane while it approaches" the British and US territories, the NHC said.
"The eye of Maria will move over the northeastern Caribbean Sea today (Tuesday), and then pass over or near the Virgin Islands overnight and Puerto Rico on Wednesday," it said.
The storm smashed into Dominica, a mountainous country of 72,000 people, late on Monday causing what Prime Minister Roosevelt Skerrit called "mind boggling" destruction. Maria was carrying 250km/h winds when it hit, the NHC said.
Mr Skerrit posted on Facebook that there were initial reports of "widespread devastation" and that the roof of his own home had been blown off.
"We have lost all what money can buy and replace," he said.
The Guadeloupe prefecture tweeted one person was killed by a falling tree and two people were missing in a shipwreck.
The region was punched just days ago by Hurricane Irma, one of the most powerful Atlantic storms on record. Irma devastated Barbuda and the US Virgin Islands of St Thomas and St John, and caused heavy damage in Cuba and Florida, killing at least 84 people in the Caribbean and the US mainland.
Maria was expected to remain an extremely dangerous category 4 or 5 hurricane until it passed near or over the Virgin Islands overnight and Puerto Rico on Wednesday, the NHC said.
Maria was predicted to be the worst storm to hit St Croix since Hugo, a Category 4 storm, in 1989.
Puerto Rico, a US territory with about 3.4 million inhabitants, avoided a direct hit from Irma two weeks ago.
Puerto Rico's governor, Ricardo Rossello, urged residents to go to official shelters.
This photo provided by the British Royal Navy shows the destruction after Hurricane Irma, in Virgin Gorda, British Virgin Islands Source: AAP
Shelters in Puerto Rico have capacity for nearly 70,000 people, but Puerto Rico Housing Secretary Fernando Gil said he was concerned that only 299 people had taken refuge in official centres as of Tuesday morning.
In Saint Martin, where nearly a third of all buildings on the Dutch half of the island were destroyed by Irma, the airport and harbour were closed ahead of Maria's approach.
'Everything is shaking'
Guadeloupe was serving as a base for aid flights to Irma-hit French territories after the hurricane, and there were fears that major damage there could hamper the relief operation.
Authorities said there were few reports of damage to buildings so far, though several areas around the largest city Pointe-a-Pitre were flooded and fallen trees were blocking many roads.
Some 40 percent of households in the territory of 400,000 are without power.
"Everything around me is shaking," former French minister Victorin Lurel told BFMTV from his home in the south of the island.
The Dominican Republic, whose east coast was battered by Irma, ordered citizens in part of the north to evacuate ahead of Maria's arrival.
St Kitts and Nevis, the British island of Montserrat, Culebra and Vieques are also on alert.
Preparing for the worst
Britain, France and the Netherlands boosted resources for the Caribbean ahead of the storm, after facing accusations that they were ill-prepared for the damage done by Irma in their overseas territories.
"We are planning for the unexpected, we are planning for the worst," said Chris Austin, head of a UK military task force set up to deal with Irma.
France said 110 more soldiers would be deployed to the region after widespread complaints of looting and lawlessness on St Martin after Irma.
This photo provided by Jenny Promeneur shows storm damage to her grandmother's tool shed/dog house, caused by Hurricane Maria in Bouillante, Guadeloupe. Source: AAP
Building supplies were hurriedly flown in to help islanders repair roofs torn off by Irma as Maria approached.
Already the island has seen a lot of rain over the past 24 hours and winds of 100 kph, according to local politician Daniel Gibbs,
"This (Maria) will not be as strong as Irma but you have to take shelter" from the storm, he said.
Hurricane series
Irma left around 40 people dead altogether in the Caribbean before churning west and pounding Florida, where the toll of deaths linked to the hurricane rose to 58 on Tuesday.
The hurricane broke records when it whipped up winds of 295 kilometres per hour for more than 33 hours straight.
French President Emmanuel Macron, speaking in New York where he is attending the UN General Assembly, said the lethal sequence of hurricanes is "one of the direct consequences of global warming".
The French leader said he had spoken to US President Donald Trump about the issue earlier Tuesday.
Macron hosted Trump in Paris in July when he sought to persuade the US leader to reconsider his decision to pull out of the Paris climate accord.
Many scientists are convinced that megastorms such as Irma, and Harvey before it, are intensified by the greater energy they can draw from oceans that are warming as a result of climate change.
