As of 11 p.m. EST, the storm was centered 280 miles east southeast of Wilmington, North Carolina, and was moving northwest at 17 mph. The NHC said the first tropical storm-force winds of at least 39 miles per hour (63 kph) would hit the region early on Thursday with the storm's centre reaching the coast Friday.
Several prominent beaches along North Carolina's southern coast closest to where Florence was expected to pass as of Wednesday morning were under the mandatory evacuation order.
With predicted rainfall measured in feet not inches, forecasters say people living along creeks and rivers in the Carolinas should move to higher ground well ahead of the storm's arrival.
While many coastal residents heeded mandatory evacuation orders, others boarded up homes and businesses and chose to courageous the storm, which is forecast to trigger severe flash flooding as it dumps as many as three feet (almost a metre) of rain in some areas.
"I encourage Georgians to be prepared for the inland effects of the storm as well as the ensuing storm surge in coastal areas", he said. But earlier this year, the Charleston County School District requested an assessment of its facilities used during hurricanes; it found the shelters should only be used for storms designated a Category 3 or below, the Charleston Post & Courier reported.
The threat has sparked a rush of evacuation efforts in SC and North Carolina, with more than a million people urged to get out of Florence's way.
Forecasters have adjusted Hurricane Florence's projected path, saying that after it makes landfall, it is likely to take a more southerly route than expected.
Some 7,000 guard members are ready to mobilize in North Carolina, while 1,100 will be activated in SC.
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People line up to enter a hurricane shelter at Trask Middle School in North Carolina.
Florence would be the strongest storm to make landfall anywhere on the East Coast since 1992, when Hurricane Andrew hit.
"The concern is about people who are very young or very old, who don't have much money or access to transportation, who do not speak the predominant language or have access to information", Thomas Tighe, of Direct Relief, said.
Officials in New Hanover County, which includes Wilmington, have stockpiled enough food and water for 60,000 people for four days, along with more than 28,000 tarps.
Florence is expected to produce total rainfall accumulations of 20 to 30 inches along the North Carolina coast - and possibly 40 inches in some spots.
Florence's intensity has diminished since it roared ashore along the USA mid-Atlantic coast on Friday as a hurricane.
"This will be a storm that's going to be far larger than we have seen in perhaps decades", Trump said. "It goes well inland". Jeff Byard of the Federal Emergency Management Agency (FEMA) invoked a former boxing champion to warn residents that it would bring "a Mike Tyson punch to the Carolina coast".
Their entire neighborhood evacuated in Wilmington, North Carolina, David and Janelle Garrigus planned to ride out Florence at their daughter's one-bedroom apartment in Charlotte. "As guests stock up, we know some of these items are selling out, but we're working around the clock to restock them as long as we safely can", the company said in a statement.