The White House has said it is likely to be the most powerful storm to strike the US in around a decade
President Obama has declared a state of emergency in Florida with deadly Hurricane Matthew bearing down on the state.
More than 1.5 million people living in low-lying areas and on the barrier islands have been told to "evacuate, evacuate, evacuate" by Governor Rick Scott, who has warned: "This storm will kill you."
The storm has claimed more than 130 lives in the Caribbean, and Florida has been warned to brace for a "catastrophic" impact from the Category 4 hurricane.
Tourist attractions including Disney World, SeaWorld and Universal Studios have been temporarily closed as a precaution, with Disney World saying the park would be closed throughout Friday.
In neighbouring Georgia, more than 500,000 people are being moved from the state's six coastal counties, along with more than 175,000 residents in parts of South Carolina.
Forecasters have warned that large waves pushed by the storm could threaten lives and buildings even before the eye reaches or even nears the shore.
White House press secretary Josh Earnest says it is likely to be the most powerful storm to strike there in around a decade.
"The preparations that we have been making in advance of the storm I think are indicative of just how serious we think it is," he told reporters.
In Haiti, 136 people have been confirmed dead and more than 3,200 homes have been destroyed.
Some 21,000 people are seeking help at 152 shelters.
Four people have also been killed in the Dominican Republic, one in Colombia and one in St Vincent and the Grenadines.
The Haitian government has estimated at least 350,000 people need help following the disaster.
Residents carry food down a street strewn with rubble in Baracoa, Cuba | Photo: PA Images
Aid groups are appealing for donations for a lengthy recovery effort to help the country's worst humanitarian crisis since the earthquake of 2010.
The hurricane is expected to hit the US east coast on Thursday night.
Even if it does not make landfall, it should still get close enough to wreak havoc along the lower part of the coast.
The last Category 3 storm or higher to hit the US was Wilma in October 2005, which killed five people, caused billions of dollars in damage and left thousands of residents without power for more than a week.
Matthew is now less than 260km south east of West Palm Beach and moving north west at 23km/h, according to the National Hurricane Centre.
The centre says it is "very difficult to specify impacts at any one location", although Florida can expect as much as 10ins of rain in some isolated areas.