The U.S. National Hurricane Center said Friday that Hurricane Dorian had strengthened into a Category 3 storm and called it "extremely dangerous.''
The storm was moving toward the northwestern Bahamas and was expected to strengthen further as it continued its expected path toward Florida.
The Bahamian government issued a hurricane watch for the northwestern Bahamas, while President Donald Trump declared a state of emergency for Florida.
The National Hurricane Center said because Dorian was moving slowly, it could produce prolonged rains, winds and storm surges, leading to life-threatening flash floods.
Dorian was moving with maximum sustained winds of 185 kilometers per hour (115 mph).
Forecasters said Dorian could slam into southeastern Florida on Monday as a Category 4 hurricane with winds of at least 209 kph (130 mph). Category 4 storms are capable of inflicting what experts describe as catastrophic damage — destroying homes and buildings, ripping up roads, and knocking down trees and power lines.
The emergency declaration for Florida paved the way for the deployment of National Guard troops and the provision of more fuel.
Florida National Guard Major General James Eifert said 2,000 troops would be mobilized in the state by late Friday, with another 2,000 joining them on Saturday.
Trump canceled a planned trip to Poland to "ensure that all resources of the federal government are focused on the arriving storm ... it's something very important for me to be here," he said Thursday. The president owns several properties in Florida, including the Mar-a-Lago resort in Palm Beach and the Trump National Doral in Miami, which Trump has suggested as a possible venue for next year's Group of Seven summit.
Officials in Florida have not yet ordered any mass evacuations because the track of the storm is still unclear. Residents in Florida have been filling their gas tanks in case they need to leave their homes.
The auto and travel group AAA said Friday that there was plenty of gas for Floridians, but that the difficulty was in getting it to retailers quick enough to keep up with the demand from drivers. Florida Governor Ron DeSantis ordered state troopers to escort tanker trucks carrying fuel to gas stations to help ensure quick delivery.
DeSantis urged residents to stock up on at least a week's worth of food, water and medicine and be prepared to lose power for days after Hurricane Dorian makes landfall.
"I think there's a pretty high degree of certainty that this is going to be a major hurricane," DeSantis said.
Orlando International Airport said it planned to shut down on Monday because of the storm.
At the Kennedy Space Center in Cape Canaveral, NASA began moving its launch platform for rockets to a giant hangar built to withstand strong winds.
The Bahamas Ministry of Tourism and Aviation said the Grand Bahama International Airport in Freeport would close Friday night and would not open again until Tuesday.
Officials in the Bahamas urged people to evacuate and seek shelter.
"Do not put your life and the life of your loved ones at unnecessary risk," said Quincy Thompson, minister of Grand Bahama, during a televised hurricane briefing.
Dorian largely spared Puerto Rico and the U.S. and British Virgin Islands, causing some floods and power outages but no major damage.