This satellite image obtained from the National Oceanic and Atmospheric Administration (NOAA) shows Hurricane Maria at 1215 UTC on September 18, 2017.
The US National Hurricane Center (NHC) said Maria had intensified to a Category Two storm as it approached the French territory of Guadeloupe, the base for relief operations for several islands hit by Irma this month.
Guadeloupe was on "red alert", with schools, businesses and government offices ordered to close, as was neighbouring Martinique, which is also part of France. Each has a population of around 400,000 people.
The hurricane, packing maximum sustained winds of 175 kilometres an hour according to the NHC, was expected to hit Guadeloupe at around midday local time (1600 GMT).
It was expected to strengthen further into a Category Three "major hurricane", the NHC warned.
Dominica, St Kitts and Nevis and the British island of Montserrat are also on alert.
French Interior Minister Gerard Collomb warned in Paris on Sunday that "we will have major difficulties" if Guadeloupe is hard hit, noting the territory was "the logistical centre from where we could supply St Martin and organise all the airlifts".
Irma killed 15 people on St Martin, an island shared by France and the Netherlands.
Officials in Guadeloupe predicted severe flooding in low-lying areas and urged residents to move to higher ground.
France, Britain and the Netherlands have been criticised for the pace of relief efforts and for struggling to contain lawlessness in their overseas territories amid widespread shortages of food, water and electricity after Irma.
But in Guadeloupe's capital, Pointe-a-Pitre, local official Josette Borel-Lincertin said authorities had ample experience of preparing for hurricanes.
"We have a culture of risk, we know what needs to be done," she said.
An additional 110 soldiers would be deployed to the region to reinforce about 3,000 people already at work tackling security problems, rebuilding infrastructure and supplying food and water to hurricane-hit islanders, he said.
He said up to 500 more people could be sent if needed.
Tropical storm warnings
Irma, a Category Five hurricane, left around 40 people dead in the Caribbean before churning west and pounding Florida, where at least 20 people were killed.
As of 1200 GMT the storm was swirling about 135 kilometres east of Martinique, according to the NHC, on track to barrel across the eastern Caribbean late on Monday and into the night.
Tropical storm warnings were in place in Antigua and Barbuda, Saba and St Eustatius, and St Lucia.
The tiny island of Barbuda was decimated by Hurricane Irma on September 5-6 when it made its first landfall in the Caribbean as a top-intensity Category Five storm.
The NHC said Maria could produce a "dangerous storm surge accompanied by large and destructive waves" that would raise water levels by 1.2 to 1.8 metres when it passes through the eastern Caribbean.
It also forecast maximum potential rainfall 51 centimetres)in the Leeward Islands, Puerto Rico and the US and British Virgin Islands through Wednesday night -- conditions that could cause life-threatening flash floods and mudslides.
A second hurricane, Jose, is also active in the Atlantic and has triggered tropical storm warnings for the northeastern United States.
Irma broke weather records when it whipped up winds of 295 kilometres per hour (183 miles per hour) for more than 33 continuous hours.
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.