Hurricane Dean bore down on Jamaica and the Cayman Islands on Sunday and threatened to pound Mexico's Yucatan Peninsula as a rare Category 5 storm.
Residents stocked up on emergency supplies and tourists crowded Caribbean airports as Dean, packing sustained winds of 145 mph (230 km per hour), headed for Jamaica as a Category 4 storm, the second-highest on the five-step Saffir-Simpson scale.
Hurricane warnings were in effect for the Cayman islands and tropical storm warnings for parts of Haiti, the Dominican Republic and Cuba.
The US National Hurricane Center said the eye of the hurricane was about 295 miles east southeast of Kingston at 2 am and was expected to be near Jamaica or to make landfall on Sunday as an exceptionally dangerous storm.
It could become a Category 5 storm after roaring by the Caymans in two days, with winds of over 155 mph (250 kph).
Dean is the first hurricane of what is expected to be an above-average 2007 Atlantic storm season.
Millions of people braced for the storm in some of the most populous areas of the Caribbean.
"If we don't manage to leave we'll go back to the hotel and barricade the hotel room and then hope and pray," said Dutch tourist Gideon Tuttezs as he waited in a standby queue to fly out of Jamaica's Montego Bay.
Jamaica's government urged people to flee low-lying and landslide-prone areas, buses were marshaled to transport evacuees and police and troops were put on alert.
"Maybe I am hoping for too much, but I only wish that the hurricane will change course," said Kingston resident Matthew Turner.
Lines formed at gas stations and supermarkets were crammed as shoppers bought batteries, flashlights, canned tuna, rice and water. Campaigning for August 27 elections was halted.
Officials in the Dominican Republic, where the hurricane sent 18-foot (5.5-metre) waves crashing onto southern beaches, first reported three deaths but later retracted two. They said a 16-year-old Haitian was swept out to sea by a wave.
Dean was moving west northwest at about 17 mph (28 kph) and it's progress was being watched closely by energy markets.
These markets have been skittish since powerful storms in 2004 and 2005 swept through the Gulf of Mexico where roughly a third of US domestic crude oil is produced. At least one production platform and two oil rigs were evacuated.
The latest computer models showed Dean slamming into Mexico's Yucatan Peninsula early in the week and then hitting the northern Mexico coast rather than threatening the most critical US offshore oil and gas production areas.
Mexican authorities began evacuations on the Caribbean coast, while US President George W Bush issued an emergency declaration for Texas to free up federal help and funds.
NASA prepared to bring the US space shuttle Endeavour, which has been on a mission to the International Space Station, back to Earth a day early on Tuesday just in case Mission Control in Houston had to close because of the storm.
Dean's destructive core was expected to pass just south of Haiti's southern coast, but the island was lashed by high winds and driving rain.
Tropical cyclones frequently trigger flash floods and mudslides in the deforested, poverty-stricken country of 8 million. Tropical Storm Jeanne in 2004 killed nearly 3,000.
In the Cayman Islands, a British territory and financial center battered by Hurricane Ivan in September 2004, national airline Cayman Airways laid on extra flights to Miami.
"I'm scared. We're trying to get out," said resident Ben Webster, who was due to leave for a holiday with his wife and daughter. "We'd rather go sooner than later."
Category 5 hurricanes are rare. Until the record-breaking 2005 Atlantic hurricane season, records showed only two years -- 1960 and 1961 -- with more than one Category 5 storm.
But in 2005, four hurricanes reached that strength -- Emily, Katrina, Rita and Wilma -- triggering debate about the impact of global warming on tropical cyclones.
(Additional reporting by Jim Loney, Michael Christie and Jane Sutton in Miami, Horace Helps and Carlos Barria in Kingston, Manuel Jimenez in the Santo Domingo, Shurna Robbins and Alan Markoff in George Town and Anna Willard in Paris)