Alarmed tourists jammed Caribbean airports for flights out of Hurricane Dean's path Saturday as the monster storm began sweeping past the Dominican Republic and Haiti and threatened to engulf Jamaica and the Cayman Islands.

The Category 4 storm's effects could be felt in Santo Domingo, the capital of the Dominican Republic, where an 11-year-old boy was killed by flying debris while watching the waves strike an oceanfront boulevard, the Dominican emergency operations center reported.

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But as dark clouds rolled in from the southeast, residents calmly ran errands at stores with fully stocked shelves, despite government advisories about heavy rains and possible flooding.

"Nothing's going to happen here — a lot of water but nothing else," said Pedro Alvajar, 61, as he sat in a doorway selling lottery tickets.

The outer bands of the storm were expected to bring as much as 6 inches of rain to the Dominican Republic and Haiti, which share the island of Hispaniola.

In Haiti, the government issued radio alerts for people in the mountains and coastal areas. In 2004, Tropical Storm Jeanne brushed the impoverished and heavily deforested country, triggering massive floods that killed 1,900 people and left 900 others missing.

In Jamaica and the Cayman Islands, which stand directly in Dean's path, fear gripped many islanders and tourists alike. Bracing for a direct hit on Sunday, Jamaica began evacuating people to more than 1,000 shelters nationwide.

Before dawn, tourists began lining up outside the Montego Bay airport in western Jamaica to book flights out. The storm was expected to bring 155 mph winds and as much as 20 inches of rain.

Shante Morgan of Moorpark, Calif., said a lack of information about the severity of the storm was fueling the fear.

"People are freaking out because they're not getting answers at their hotel," said Morgan, 38, who got a Saturday flight after waiting several hours. "They're really playing down the potential influence of the hurricane."

Jamaican Prime Minister Portia Simpson Miller called for a halt to campaigning for the Aug. 27 general elections, saying: "Let us band together and unite in the threat of this hurricane."

Michelle Edwards, of Jamaica's Office of Disaster Preparedness and Emergency Management, said people in vulnerable communities across the island will be moved to schools and other shelters.

Further west in the low-lying Cayman Islands, lines of tourists waiting for flights snaked out of the international airport terminal and onto the lawn outside. Many tourists flopped under a tree to get out of the sun, surrounded by their luggage.

Cayman Airways added 15 flights to Florida from the wealthy British territory, and they were quickly sold out. The islands were expected to take a direct hit on Monday.

Dean, the first hurricane of the Atlantic season, gained strength over warm Caribbean waters after claiming six lives and devastating banana and sugar crops when it hit tiny islands in the eastern Caribbean on Friday as a Category 2 storm.

As of 5 p.m. Saturday, Dean was centered about 165 miles south of Santo Domingo and 450 miles east-southeast of Kingston, Jamaica. It was moving west at 18 mph and had maximum sustained winds near 150 mph.

The storm was expected to clip Mexico's Yucatan Peninsula and enter the Gulf of Mexico by Tuesday, according to the National Hurricane Center in Miami.

Authorities on Mexico's Caribbean coast began evacuating tourists and residents from low-lying Holbox island north of Cancun on Saturday. A total of 2,200 people, including some 250 Mexican and foreign tourists, were ordered to leave, state officials said.

Forecasters said it was too soon to say whether the hurricane would strike the United States.

Worried the storm could disrupt operations at Mission Control in Houston, however, NASA shortened the last spacewalk for astronauts aboard the shuttle Endeavour and ordered the spacecraft to return to Earth a day early on Tuesday.

President Bush, meanwhile, signed a pre-landfall emergency disaster declaration for Texas, allowing the federal government to immediately send people, equipment and supplies to the state if Dean makes landfall there.

In Cuba, which could get rain from the outer bands of the storm, the government issued a tropical storm warning and said it was evacuating 50,000 people from three provinces.

Dean passed near the islands of St. Lucia and Martinique early Friday as a Category 2 storm with winds near 100 mph.

In St. Lucia, fierce winds tore corrugated metal roofs from dozens of homes and the pediatric ward of a hospital, whose patients had been evacuated hours earlier. Police spokeswoman Tamara Charles said a 62-year-old man drowned when he tried to retrieve a cow from a rain-swollen river.

In Dominica, a woman and her 7-year-old son were killed when a rain-soaked hillside gave way and crushed the home where they were sleeping, said Cecil Shillingford, the national disaster response coordinator. Dominica's government reported at least 150 homes were damaged.

Authorities said two people died on the French island of Martinique, including a woman who apparently fell and drowned.