Haiti and Jamaica have implored residents in coastal areas to leave and Cuba has suspended flights as Hurricane Matthew spun slowly toward the region.
Matthew is the strongest storm to menace the Caribbean islands since 2007 and is expected to scrape western Haiti on Monday, bringing 230km/h winds and life-threatening rain to the southern coast, while simultaneously lashing Jamaica.
Eastern Cuba also will feel bands of fierce wind and rains on Monday, the US National Hurricane Center said.
The category four storm was about 475 southeast of Kingston on Sunday afternoon (Monday morning AEST).
"Slow motion is almost always a bad thing for any land area impacted," said John Cangialosi, a hurricane specialist at the centre, noting the storm's devastating rains and winds would linger over the region.
With tropical storm conditions expected to reach Haiti and Jamaica late on Sunday, officials in both countries have urged residents to prepare.
In Haiti, the prime minister's office issued a red alert warning for landslides, high waves and floods.
Matthew is the most powerful hurricane to form over the Atlantic since Felix in 2007 and up to 101cm of rain could fall on parts of southern Haiti, triggering deadly flash floods and mudslides.
Despite worries about storm devastation, life in the southern Haitian town of Les Cayes continued as normal, residents said.
"If it passes by here, that's when I protect myself," said Jean Robert, 40, who leaned against a motorcycle outside of the bank where he works.
"I have no preparation. I have nothing."
In Jamaica, the government of Prime Minister Andrew Holness was preparing buses to help evacuate Port Royal at the vulnerable edge of Kingston Harbour.
Holness told Reuters before the first lashings of rain that his government was mobilised and about 80 per cent of the 2.7 million Jamaicans were ready for the storm.
In Cuba, where evacuations already were well under way, with many flights were suspended as of noon on Sunday.
Cuban President Raul Castro warned that Matthew was stronger than Hurricane Sandy, which devastated Santiago de Cuba in 2012.
"We have to prepare as if it has twice the power of Sandy," Castro was reported as saying in the Granma newspaper.
A few kilometers east, the US was flying about 700 spouses and children to Florida from its Guantanamo Bay naval base, while prisoners and service personnel will remain.
Matthew could affect the Bahamas and the US east coast later in the week.
