The category four hurricane was already dumping inches of rain on the island, and roads were blocked by fallen trees and flooded in eastern parts pf the island, with power cuts affecting thousands of homes.

"The sea has dumped debris onto the roads," Portland parish Mayor Bobbie Montague said.

By 2100 GMT, the hurricane was scraping Jamaica's southern coast and lay just 50 miles (80 kilometers) from the capital Kingston moving at about 20 miles (32 kilometers) an hour, the US National Hurricane Center warned.

Packing winds of up to 145 miles (230 kilometers) an hour, Hurricane Dean "has the potential to become a category five hurricane in the northwestern Caribbean sea tomorrow (Monday)" -- the top strength in the scale.

"Preparations to protect life and property in Jamaica should already have been completed. Preparations in the Cayman Islands should be rushed to completion," the center's latest hurricane report said.

It added Dean could unleash as much as 20 inches of rain on the island in the coming hours, and warned waves could surge seven to nine feet (two to three meters) above normal tide levels.

Jamaica's airports were shut Saturday, and hundreds of people have packed into the 1,000 shelters opened up by the government around the island amid bitter memories of Hurricane Ivan which killed 14 people in 2004.

Prime Minister Portia Simpson Miller called on all off-duty police officers, firefighters and prison warders to report for work, while the electricity provider was shutting down the national grid as a safety measure.

The Jamaica Public Service said more than 135,000 customers were without power.

There were also fears for some 17 people, believed to be Spanish divers, who had refused to leave the small sandbank of Pedro Cays, some 50 miles (80 kilometers) south of Jamaica, lying directly in Dean's path.

"It would be impossible for any rescue operation to take place now," said Captain Havland Honnigan, chairman of the Fishermen Co-Operative in the town of St. Elizabeth.

Mexico was meanwhile evacuating thousands of tourists as well as its oil platforms in the Gulf of Mexico, with Dean set to slam into the Yucatan peninsula late Monday.

A leading insurance company, Eqecat Inc. on Sunday estimated initial losses in the Lesser Antilles islands and Jamaica at between 1.5 billion and three billion dollars.

Hurricane Dean earlier brushed past Haiti, lashing it with heavy rain and gale-force winds.

Two people were killed in Haiti's southeastern Moron and southern Tiburon towns, and four people caught on a sailing boat were injured, Haitian officials said.

Environment Minister Jean Marie Claude Germain, who was heading to the devastated areas, told AFP there had been huge damage to agricultural plantations because the trees had been cut down.

"It is not in our culture to protect the environment, and today we are beginning to see the need to put in place policies to reforest our country and find an alternative to burning wood, which is one of the main causes of the deterioration of the environment," he said.

More than 1,000 people were evacuated from low-lying areas in Haiti, one of the world's poorest countries.

Two people were also killed in the French territory of Martinique, while authorities in the Dominican Republic, where a 16-year-old boy was killed when he was swept away by huge waves, warned of the danger of landslides.

"Residents on the south coast are advised to take precautions against landslides," the National Emergency Committee said.

It added that 1,580 people had been evacuated and some 316 houses had been damaged, many of them severely.

In Cuba just to the north of Jamaica, authorities had evacuated some 150,000 people from six eastern provinces to save them from possible flooding.

In Mexico, the state oil company PEMEX began evacuating some 13,360 workers from more than 140 oil platforms, using 55 boats and 29 helicopters, it said in a statement.

Some 90,000 tourists were also being evacuated from Cancun and other popular barrier islands of the "Mayan Riviera" after authorities blocked all new tourist arrivals.

In 2005, Wilma, one of the strongest hurricanes ever, made a direct hit on Cancun and Cozumel and held over the area for hours, wiping out hotels and beaches that have still not been totally rebuilt.

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