Florence has rapidly strengthened into a category 4 hurricane as it closes in on North and South Carolina, carrying winds and water that is also predicted to wreak havoc over a wide stretch of the eastern US later in the week.
The governors of both North and South Carolina states, as well as Virginia have declared states of emergency.
South Carolina Governor Henry McMaster ordered the evacuation of the state’s entire 300-kilometre coastline beginning at later Tuesday.
“This is a real hurricane we have coming,” Mr McMaster said. “We don’t want to risk one South Carolina life.”
Hurricane Florence had already begun battering barrier islands off the US coast, creating dangerous rip currents and sending seawater over the state highway.
For many ordered to evacuate, the challenge could be finding a safe refuge: If Florence slows to a crawl just off the coast, it could carry torrential rains up into the Appalachian mountains, causing flash floods, mudslides and other dangerous weather across a wide area.
Florence has already reached top sustained winds of 195 km/h.
By Monday afternoon it was centred about 1985km east-southeast of Cape Fear, North Carolina, and moving west at 20 km/h.
Its centre will move between Bermuda and the Bahamas on Tuesday and Wednesday, and approach the coast of South Carolina or North Carolina on Thursday, the National Hurricane Centre said.
Hurricanes Isaac, which could hit Caribbean islands, and Helene, much farther out to sea, lined up behind Florence as the 2018 Atlantic season reached its peak.
President Donald Trump cancelled a rally that was planned for Friday in Jackson, Mississippi, because of safety concerns, his campaign organisation said.
Navy ships off Virginia’s coast were preparing to sail out of the path, a North Carolina university has already cancelled classes and people have begun stocking up on plywood, bottled water and other supplies.
Red flags have already been flying on beaches, warning swimmers to stay out of the water as seas began kicking up.
People rushed to get emergency kits ready, map out escape routes, fill sandbags and secure their homes.
“Pretend, assume, presume that a major hurricane is going to hit right smack dab in the middle of South Carolina and is going to go way inshore,” Mr McMaster said.
The state’s emergency management agency said it is “preparing for the possibility of a large-scale disaster.”