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As of Monday 2 a.m. (local time), Maria was about 145 km north-northeast of Barbados and about 270 km east-southeast of Dominica, the US-based National Hurricane Center said.
"Maria continues to strengthen and is expected to be at 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 Center said.
Maria is one of three storms churning in the Atlantic Ocean, but it poses the most danger to the hurricane-battered Caribbean, CNN reported.
Maria has prompted a hurricane warning for Martinique, Guadeloupe, Dominica, St. Kitts, Nevis and Montserrat.
A tropical storm warning is in effect for Antigua and Barbuda, Saba, St. Eustatius and St. Lucia.
A hurricane watch is in effect for the US Virgin Islands, the British Virgin Islands, St. Martin, St. Barthelemy and Anguilla.