The storm continues to intensify before hitting the Leeward Islands and the northeastern Caribbean Sea Monday night. Last week's powerful Hurricane Irma left at least 84 people dead.
Hurricane Maria has strengthened into a major hurricane; the second powerful storm in as many weeks bearing down on a string of battered Caribbean islands.
Maria is expected to intensify further as it moves through the Leeward Islands and the northeastern Caribbean Sea, the US National Hurricane Center (NHC) said on Monday.
Maria, now a Category 3 hurricane on the five-step Saffir-Simpson scale, was about 150 kilometres (95 miles) east-southeast of Dominica and was carrying maximum sustained winds of 195 kilometres per hour (120 miles per hour), it said.
"The centre of Maria will move across the Leeward Islands on Monday night, over the extreme northeastern Caribbean Sea Tuesday and Tuesday night, and approach Puerto Rico and the Virgin Islands on Wednesday," the NHC added.
The government of Puerto Rico has already begun preparations for Maria, which is expected to make landfall there on Tuesday, officials said on Sunday.
Hurricane warnings issued
Hurricane warnings were in place for Dominica, St. Kitts, Nevis and Montserrat, St. Lucia and the French overseas departments of Guadeloupe and Martinique.
Tropical storm warnings were in effect for Antigua and Barbuda and the Dutch Caribbean territories of Saba, St Eustatius and St. Maarten, while Puerto Rico, the British and US Virgin islands, and Anguilla were on a watch for hurricane conditions.
Several of those islands were devastated earlier this month when Hurricane Irma rampaged through the Caribbean as one of the most powerful Atlantic hurricanes ever recorded, killing more than 80 people on the islands and the US mainland.
More than 1,700 residents of Barbuda were evacuated to neighbouring Antigua after Irma damaged nearly every building there.
Irma killed at least 84 people, more than half of them in the Caribbean.
Tropical storm Jose
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 535 km southeast of Cape Hatteras, North Carolina.
The eye of Jose, with top sustained winds of 150 km per hour, 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.
Up to five inches of rain could fall over parts of the area, and the storm could bring dangerous surf and rip currents as well.