Hurricane Dorian threatening the Bahamas and the US south-eastern coast has strengthened to category four, the US National Hurricane Center (NHC) says.
Dorian has maximum sustained winds of nearly 145mph.
The hurricane is expected to grow even stronger, its center potentially crossing the Bahamas before skirting Florida’s east coast early next week.
Reports from the Bahamas described tourists scrambling to leave before the closure of the international airport.
In Florida, Governor Ron DeSantis has declared state of emergency for the whole state and urged residents to stock enough food, water and medicine to last at least a week.
According to forecasters, Dorian could be the region’s worst storm since category five Hurricane Andrew killed 65 people and destroyed 63,000 homes in 1992.
President Donald Trump said he was monitoring Dorian, which he described as “an extremely dangerous storm” on Twitter.
Hurricanes, whose strength can range from category 1 to 5 on the Saffir-Simpson scale, tend to get stronger as they move over warm waters like those off Florida.
By the middle of next week, forecasters expect the hurricane to shift eastwards, putting the coasts of Georgia and South Carolina at risk.
“Dorian is anticipated to remain an extremely dangerous major hurricane while it moves near the north-western Bahamas and approaches the Florida peninsula into early next week,” the NHC said.
The NHC warned that Dorian could cause “incredibly catastrophic damage”.
In an advisory on August 31, the NHC said Dorian was not expected to make landfall in Florida but the possibility that it will cannot be ruled out.
“Life-threatening storm surge and devastating hurricane-force winds are still possible along portions of the Florida east coast by the early to middle part of next week,” the NHC said.
Residents of Georgia and South Carolina have been told to keep an eye on the forecast as Dorian churns towards the US coast.
Dorian’s exact path toward Florida remains uncertain but millions of people could be affected, as well as holiday attractions such as Walt Disney World and President Donald Trump’s Mar-a-Lago resort.
Dorian is expected to drop up to 12in of rain on the coastal US, with some areas getting as much as 18in. Tides in the region are already at some of their highest levels of the year, owing to a naturally occurring event.
A new moon, combined with the coming autumn equinox, has created what are known in Florida as “king tides”. These are likely to exacerbate dangerous levels of flooding, forecasters warn.
Florida governor has activated 2,500 National Guard troops, with another 1,500 on standby.
Shoppers in Florida have been queuing around the block to snap up supplies such as medication and fuel. Some petrol stations reported fuel shortages, while a few shops had run out of bottled water.
The coastal city of Miami ordered the removal of electric rental scooters from the streets to avoid any potential hazards.
Officials fear the rental scooters, operated by firms such as Lime, Lyft and Uber’s Jump, could be swept away by strong winds, turning them into projectiles.
No immediate mass evacuations have been ordered by state authorities but President Trump, who had warned that Dorian “could be an absolute monster”, said a decision could be made on Sunday.
People have been asked to bring their pets with them in case of evacuation. On social media, the names of hotels that accept pets are being shared.
Orlando International Airport announced it was halting commercial flights from 02:00 on September 2 “out of an abundance of caution”. Tourist resorts in the city remained open, however.
President Trump canceled a planned trip to Poland because of the storm, sending Vice-President Mike Pence instead.