Hurricane Matthew has strengthened as it moves slowly towards Florida, and is set to be the strongest storm in the US for 12 years.
With winds of 125mph (205km/h), it is expected to hit Florida early on Friday as a Category Four storm.
At 20:00 local time (01:00 GMT), it was 75 miles offshore of West Palm Beach.
The hurricane has pounded the Bahamas after devastating parts of Haiti, where at least 264 people have been killed and thousands displaced.
Four people were also killed in the neighbouring Dominican Republic.
Damage could be “catastrophic”, Florida’s governor said. More than two million people have evacuated in the US.
As of 20:00 GMT, the storm was passing over the far west of the Bahamas, having battered the capital, Nassau. All air and sea traffic has been halted and people urged to move to higher ground because of storm surges.
Hurricane Matthew has been upgraded into a Category Four storm, the second-highest classification.
It is expected “move very close” to the east coast of the Florida peninsula in the next twelve hours, the US National Hurricane Center (NHC) said.
States of emergency have already been declared in four southern states, allowing the National Guard to be deployed. On Thursday afternoon, President Obama declared a state of emergency for Florida and South Carolina, allowing federal emergency teams to be sent.
Matthew could be the first Category Four storm to make landfall in the United States since Charley in August 2004, that caused $14bn (£11bn) in southern states.
“There are no excuses, you need to leave,” Florida Governor Rick Scott warned everyone in evacuation zones.
“If you’re reluctant to evacuate, just think of all the people this storm has already killed. You and your family could be among these numbers if you don’t take this seriously.”
“Everyone in our state must prepare now for a direct hit,” Governor Scott told reporters.
“If Matthew directly impacts Florida, the destruction could be catastrophic and you need to be prepared.”
Some two million people have been advised to evacuate across coastal areas of Florida, Georgia and South Carolina. North Carolina could also be affected as the storm moves north.
The NHC warned that coastal waters in parts of Florida could rise by up to 11 feet (3.35 metres) because of a storm surge – when ocean surface water rises as a result of high winds, and is pushed on to coastal areas.
n many areas, cars queued for fuel and residents stocked up on food and hardware supplies to board up their houses, local reports said.
Schools, universities and government offices in some areas are closed. About 90% of flights coming through Miami’s airports were cancelled by mid-morning, airport officials said, with other airports also affected.
In South Carolina, lanes on some highways have been reversed so vehicles can head west away from the storm.
In Haiti, meanwhile, rescue workers are struggling to reach areas cut off by the storm.
Officials said they were not yet in a position to gauge the true extent of the damage – particularly in the Grand Anse area, which was directly in the storm’s path.
A key bridge had been destroyed, roads were impassable and phone communications were down, officials said.
Mourad Wahba, the UN special representative for Haiti, said at least 10,000 people were in shelters and hospitals were overflowing.

Source: BBC