The National Hurricane Center upgraded Hurricane Dorian to a Category 5 storm on Sunday with sustained winds reaching 160 mph. The centre added that the hurricane was about to hit the Abaco Islands in the northern Bahamas.
The day before, Bahamas Prime Minister Hubert Minnis urged residents to evacuate to the main island.
"I want you to remember: homes, houses, structures can be replaced. Lives cannot be replaced," he told a news conference.
On Friday, US President Donald Trump issued an emergency declaration for Florida and "ordered federal assistance to supplement state, tribal and local response efforts."
Authorities in North and South Carolinas that may also be hit by the hurricane have declared a state of emergency but have held off mass evacuations due to uncertainty over the hurricane's path.
Meanwhile, another storm that will become a hurricane on Monday has formed southwest of Mexico.