Jamaicans prepare for the arrival of Hurricane Dennis

The Cayman Islands and Cuba also were under hurricane warnings, including the U.S. detention camp holding some 520 terror suspects in Guantanamo Bay.

In Haiti, rivers burst their banks flooding some areas.

There were no immediate reports of casualties.

About 6,000 people died in floods in Haiti last year.

Dennis strengthened into a hurricane Wednesday and became a Category 2 storm Thursday morning, becoming the third storm to threaten petroleum output in the Gulf of Mexico.

In Jamaica, the Prime Minister Percival Patterson called on everyone on the island "to put in place measures to protect the elderly, infirm, the disabled and the young."

Cancelled

Authorities said they activated an Emergency Disaster Plan and warned residents of likely power cuts and disruptions in drinking water supplies.

Flights in and out of Jamaica were cancelled.

Community Development Minister Portia Simpson Miller said soldiers and police were put on alert to prevent looting.

She said: "We will not tolerate criminal activity of any kind during this period and the security forces have pledged to be efficient."

Dennis came right behind Tropical Storm Cindy, which made landfall late Tuesday in Louisiana and hindered oil production and refining.

Forecasters said it was the first time the Atlantic season had four named storms this early since record-keeping began in 1851.

The Atlantic hurricane season runs from June 1 to Nov. 30.