MIAMI (REUTERS) - A second powerful storm in as many weeks was bearing down on a string of battered Caribbean islands, with forecasters saying that Maria had strengthened into a hurricane on Sunday (Sept 17) and would intensify before hitting the Leeward Islands on Monday night.

"Maria... could be near major hurricane intensity when it affects portions of the Leeward Islands over the next few days, bringing dangerous wind, storm surge and rainfall hazards," the US National Hurricane Centre (NHC) said.

Maximum sustained winds are expected to accelerate to 193kmh within 72 hours, by which time the hurricane could reach the British and US Virgin Islands and Puerto Rico, a US territory with a weakened economy and fragile power grid.

The government of Puerto Rico has already begun preparations for Maria, which is expected to make landfall there on Tuesday, officials said.

The storm is moving west-northwest at about 24kmh and is expected to cross the Leeward Islands on Monday night, the NHC said.

Hurricane warnings were in place for the French island of Guadeloupe, Dominica, St Kitts, Nevis and Montserrat, while a hurricane watch was in effect for US Virgin Islands, British Virgin Islands, Saba and St Eustatius, St Maarten, St Martin and St Barthelemy, and Anguilla.

A tropical storm warning was in effect for Antigua and Barbuda, St Lucia and Martinique.

Maria is approaching the eastern Caribbean less than two weeks after Irma hammered the region before overrunning Florida.

That storm, one of the most powerful ever recorded in the Atlantic, with winds up to 298kmh, killed at least 84 people, more than half of them in the Caribbean.

The NHS also issued a tropical storm watch for portions of the US mid-Atlantic and New England coast by Tuesday, as a second hurricane, Jose, moved slowly north from its current position in the Atlantic Ocean about 535km south-east of Cape Hatteras, North Carolina.

The eye of Jose, with top sustained winds of 150kmh, should remain off the US East Coast, the NHS said.

Even so, by Tuesday, it could bring tropical storm conditions from Fenwick Island, Delaware, to Sandy Hook, New Jersey, and from East Rockaway Inlet on New York's Long Island to the Massachusetts island of Nantucket.