Hurricane Dean is sweeping past Haiti and the Dominican Republic, as people in the two countries face a battering by heavy rains and flooding.
An 11-year-old boy died in the Dominican Republic, bringing the hurricane's death toll so far to four.
Jamaica is now bracing itself for a direct hit from the storm on Sunday.
Winds are currently 233km/h (145mph) and the storm may achieve the highest category, five, by the time it reaches Mexico on Monday.
Forecasters warn this could be an unusually active Atlantic storm season.
In the US, Louisiana has declared a state of emergency, though the chances of the storm hitting are slim.
Governor Kathleen Blanco took the decision amid heightened sensitivity to hurricanes since Katrina flooded New Orleans in 2005.
The neighbouring state of Texas categorised Dean as an imminent threat, and US President George W Bush issued an emergency declaration allowing federal funds to be released for the state.
The hurricane is passing to the south of Hispaniola, the island shared by Haiti and the Dominican Republic.
Haiti has issued an alert for coastal communities and ordered fishing boats to stay ashore until after the weekend.
Rough waves damaged buildings on the coast of the Dominican Republic, and a boy was reported drowned and several people were injured in the capital Santo Domingo.
Meanwhile Jamaica has ordered emergency shelters to be opened and Prime Minister Portia Simpson-Miller called for a halt to campaigning for the elections on 27 August.
"Let us band together and unite in the threat of this hurricane," the prime minister said.
But experts warned that the hurricane would be made worse by exceptional rainfall and coastal storm surges.
"It has the potential to be almost catastrophic," Dennis Feltgen from the US National Hurricane Center told the BBC.
"...Precautions on the island of Jamaica need to be rushed to completion to protect life and property."
US hurricane monitors have also urged the Cayman Islands to be vigilant.
The hurricane is due to reach the Gulf of Mexico, where the US has much of its domestic oil and gas supplies, on Monday.
Some companies have already begun shutting down production platforms and evacuating workers to the mainland.
"This storm is moving faster than the average storm," Rebecca Waddington of the National Hurricane Centre in Miami told the BBC's World Service.
"It is forecast to have a direct hit on Jamaica at a Category Four strength, which is an extremely dangerous storm [and is forecast to come] very close to the Mexican coast, near the Texas-Mexico border."
Dean earlier visited destruction on the islands of St Lucia, Martinique and Dominica, with roofs ripped off and banana plantations flattened.
In Dominica, a landslide crushed a woman and her seven-year-old son while they slept in their home.
In St Lucia, a 62-year-old man was swept away and drowned when he tried to retrieve a cow from a rain-swollen river.