Governor Ron DeSantis of Florida on Thursday expanded the state of emergency declaration he issued for 26 counties to one that covers all of the 67 counties in the state "due to hurricane Dorian's uncertain projected path", Xinhua news agency reported.
"All residents, especially those along the east coast, need to be prepared for possible impacts," DeSantis said in a statement.
DeSantis added that he has activated more than 2,500 Florida National Guard troops.
Governor Brian Kemp of Georgia declared a state of emergency in 12 counties in the southern coastal area of the state.
Urging residents in Georgia "to be ready to move quickly," Kemp said little is known about "the initial or the path that the storm will take", but more information will come within the next 24 hours.
"There's a lot of moving parts right now that our counterparts in Florida are dealing with, and then we're also preparing as well for whatever happens," he added.
According to the latest forecast by the National Hurricane Centre (NHC) issued at 5 p.m. on Thursday, Dorian, now near the Bahamas, is still a Category 1 hurricane with maximum sustained winds of 140 km per hour. It is moving northwestward near 20 km per hour.
The NHC expected Dorian to strengthen to a Category 4 hurricane with peak winds of 209 km per hour by Sunday, possibly making landfall by September 2 in the east coast of Florida.
According to forecasters, Dorian could be the strongest direct hit to Florida's east coast since hurricane Andrew in 1992.
President Donald Trump said on Thursday that he decided to cancel a planned trip to Poland during the weekend and stay in Washington "to ensure that all resources of the federal government are focused on the coming storm".
Speaking at the Rose Garden of the White House, Trump said Vice President Mike Pence will travel in his place.
"It's something very important for me to be here. The storm looks like it could be a very, very big one indeed."
Meanwhile, airlines have cancelled 83 flights to, from and within the US, according to FlightAware.com.
Seventy-eight flights were cancelled Thursday and five have been cancelled for Friday.
More flights were likely to be cancelled on Sunday.
( With inputs from IANS )