Hurricane Dorian strengthen into an “extremely dangerous” storm as it barrels towards the US, the National Hurricane Center (NHC) has said.
Dorian is now a Category Three hurricane.
The storm is expected to hit Florida as a 130mph (209km/h) category four.
Forecasters warn it could be the state’s deadliest storm since category five Hurricane Andrew killed 65 people and destroyed 63,000 homes in 1992.
Dorian is projected to make landfall on Monday, which is Labor Day, a public holiday in the US.
The storm is moving slowly – at just 12mph (19km/h) as it crawls north-west across the ocean surface.
Hurricanes tend to get stronger as they move over warm water like that off the Florida coast.
The NHC warned in a briefing that Dorian could cause “incredibly catastrophic damage” with life-threatening storm surges of up to 9ft (2.7m).
The hurricane was expected to drop up to 12in (30cm) of rain on the coastal US, with some areas getting as much as 15in.
The NHC has issued a hurricane watch for the north-western Bahamas, warning that heavy rain “may cause life-threatening flash floods”.
Dorian earlier this week grazed the US territory of Puerto Rico, battering its smaller islands, Vieques and Culebra, with heavy rain and high winds.
Florida’s Governor Ron DeSantis has declared a state of emergency for the whole state.
He told residents: “We urge all Floridians to have seven days worth of food, medicine, and water.
“This is potentially a multi-day event where it will churn slowly across the state. That obviously creates a whole host of issues.”
The governor has activated 2,500 National Guard troops, with another 1,500 on standby.
Shoppers in Florida have been queuing round the block to snap up supplies such as medication and fuel.
People have been asked to bring their pets with them in case of evacuation, and on social media, the names of hotels that accept pets are being shared.
US President Donald Trump warned Dorian “could be an absolute monster”. He canceled a planned trip to Poland because of the storm, sending Vice-President Mike Pence instead.
Trump’s critics have argued that he is only taking the hurricane seriously now because it is threatening white people on the US mainland.
A Democratic congressman, Don Beyer of Virginia, said that the Republican president took notice because “Florida is not an island full of people of color”.