Hurricane Wilma is battering the leading resorts of Mexico's Yucatan peninsula, where tens of thousands of people have moved to safety.
Hurricane Wilma is expected to linger over the Yucatan until Sunday
The centre of the powerful Category Four storm is now over the island of Cozumel and is moving slowly towards the north-east of the peninsula.
Heavy rains and mudslides triggered by Wilma have killed at least 13 people in the Caribbean, mostly in Haiti.
The storm is expected to weaken before hitting Florida on Sunday or Monday.
The eye of the hurricane is passing directly over the island of Cozumel, the Mexican weather service said.
In Cozumel and Cancun, power has been knocked out, road signs torn down and waves have flooded the deserted streets.
With Yucatan airports now closed, tens of thousands of tourists in the area have been moved inland or are now taking cover from sustained winds of 140mph (225km/h).
Mexican President Vicente Fox has urged people to remain in shelters set up in schools and gymnasiums.
"The most important thing now... is to protect lives," he said in a televised speech.
One shelter reportedly flooded overnight and some 300 people had to be relocated. Others are said to be cramped and hot, without electricity to power air conditioning.
Officials have warned the centre of the storm could linger over the peninsula until Sunday morning.
"Tin roofing is flying through the air everywhere. Palm trees are falling down, Signs are in the air and cables are snapping," Julio Torres of the Cozumel Red Cross told the Associated Press news agency.
The BBC's Claire Marshall, in Cancun, says holidaymakers are abandoning the resort, which is built along a narrow beach of white sand that could be vulnerable to the predicted 10ft (3m) storm surge of sea water.
The hurricane has also been causing heavy wind and rain in western Cuba.
US forecasters warn the Yucatan and isolated areas of Cuba could see 25 to 50cm (10 to 20in) of rain by Sunday, with some parts of Cuba hit by up to 100cm (40in).
Schools have been closed and storm drains cleared as a precaution in the capital, Havana, even though it should not be directly affected.
The Cuban government says 370,000 people have been ordered out of the hurricane's path.
In Florida, Governor Jeb Bush has declared a state of emergency, although mandatory evacuations for Florida Keys residents were put back, as Wilma's slow speed means it may not arrive until Monday.
"Both the location and the timing of the impacts on Florida remain very uncertain," US National Hurricane Center (NHC) forecaster Richard Knabb said.
2005 has been one of the most destructive hurricane seasons on record. Wilma is the 12th of the year - a figure equalled only once, in 1969, since record-keeping began in 1851.
By one measure, Wilma was the strongest ever, with the lowest barometric pressure on record in the Atlantic basin.
It has since dropped in strength from Category Five to Category Four, but the NHC has warned it is expected to regain strength soon.
Thousands of people have died in Central America this month from landslides and floods following torrential rains brought by Hurricane Stan.
Mexico: Tourists told to leave high-risk coastal resorts
Cuba: Coastal residents evacuated and some schools closed
US: Visitors and non-residents ordered to leave Florida Keys
Times: All times GMT