Hurricane Dorian moved northwest on Saturday, churning slowly across the Atlantic in the direction of Georgia and the Carolinas, with Florida also still in its sights.
Authorities representing beach communities along Florida's east coast told residents to stay alert, although latest forecasts indicate they may dodge a direct hit from the dangerous category 4 storm.
The Miami-based National Hurricane Center said there had been a "notable change" since Friday night, with the latest forecasts showing the eye of the storm could veer north and stay out at sea.
But it warned that its course remained unpredictable and Dorian posed an immediate threat to the Bahamas as well as millions of people along the southeast US coast.
The NHC said Dorian was packing maximum sustained winds of 240km/h and was expected to hit the northwest Bahamas islands on Sunday and be near Florida's east coast late Monday through Tuesday.
Bahamas tourist hotspots Great Abaco and Grand Bahamas are predicted to get up to two days of hurricane-force winds as Dorian slows to a 3.2km/h crawl.
"This is a very dangerous situation for the Bahamas," NHC Director Ken Graham said in a Facebook Live video.
After previous focus on a possible Florida landfall, Graham said other southeast US states now had to be on alert.
"Georgia, North Carolina and South Carolina have got to pay attention as well," he said.
The governors of Florida, Georgia and North Carolina have all declared states of emergency.
On Florida's east coast, popular surfing spot Cocoa Beach was quiet as tourists stayed away, while locals worked on putting up hurricane shutters and buying supplies ranging from water to power generators.
Concerns grew further up the coast as NHC models on Saturday showed there was a two-thirds chance the hurricane could hit land as far north as the North Carolina-Virginia state line.
"I was going to go north, but it's going to South Carolina, and now I don't know what it's doing," said Andrea Greenleaf, 25, a freelance photographer in Jacksonville, Florida.
Ashley Rew, a 44-year-old housekeeper, said local hotels lost hundreds of bookings after a college football game was moved from Jacksonville to Tallahassee due to the storm.
"I've bought five cases of water, filled my car up, I have a lot of bread and food and canned items," said Rew, who planned to head to her mother's house in Atlanta if things got "really bad".
In the Bahamas, most tourists who planned to leave had already gone after Freeport's international airport shut down on Friday night.
Southern Florida towns urged residents to remain alert despite NHC maps indicating the storm might wobble up the coast instead of hitting land.
"Don't start taking down your shutters, don't start disassembling your emergency plan because there's still a high likelihood we'll get tropical-storm-force winds," said Eric Flowers, a spokesman for the sheriff's office in Indian River County. "There's still a potential for evacuations, we'll make that decision after the 5pm update."