The first tropical storm-force winds were forecast to hit the coast on Thursday.
"This storm will bring destruction", said North Carolina Governor Roy Cooper.
Given the storm's size and slow speed, officials warned that Florence could cause similar large-scale flood damage to that seen in the Houston area during Hurricane Harvey just over a year ago.
As Hurricane Florence pummeled the Carolinas with life-threatening storm surge, high winds and relentless rain Friday morning, FEMA administrator Brock Long issued a stark warning: "It's only going to get worse at this point".
The police chief of a barrier island in Florence's bulls'-eye said he was asking for next-of-kin contact information from the few residents who refused to leave.
The expected heavy rainfall would produce both flash flooding and river flooding that could in turn cause an environmental disaster, if the water inundates the region's many industrial waste sites and hog manure ponds.
The city of Jacksonville's statement says people have been moved to the city's public safety center as officials work to find a more permanent shelter.
What also makes Florence extremely risky are the deadly storm surges, mammoth coastal flooding and historic rainfall expected far inland.
Rescue workers in North Carolina meanwhile were scrambling to save people stranded in their homes. Forecasters warn it will bring "catastrophic freshwater flooding", according to the National Hurricane Center.
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Hurricane Florence Is a ‘Horrific Nightmare’ to Predict, Says Forecaster
It's forecast to gradually turn toward the northeast on Friday and then accelerate northeastward over the weekend. First responders in North Carolina are scrambling to rescue residents stranded in the coastal town of New Bern.
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The National Hurricane Center says the Neuse River near the city is recording more than 10 feet (3.05 meters) of inundation. "The water looming over Dr. Navarro is a brilliant way of showing the dangers of storm surge".
Here's what you need to know.
"Even after Hurricane Florence makes landfall, it's still forecast to just crawl west over SC, gradually weakening to a tropical storm", said FOX 46 Meteorologist Tara Lane.
As of 4 a.m., Florence was 30 miles (45 kilometers) east of Wilmington, North Carolina.
"The deepest water will occur along the immediate coast in areas of onshore winds, where the surge will be accompanied by large and destructive waves".
Power suppliers report more than 350,000 outages in North Carolina, the bulk along the coast.
Wilmington, North Carolina, just north of where Florence appeared headed for shore, grew empty and quiet on Wednesday.
With Hurricane Florence, numerous coastline will see water levels from the storm surge rise over 3 feet, with some families seeing over 9 feet of water near their homes.
Hurricane Florence's outer edges have started to batter the coast of North Carolina - with winds of 100mph bending trees and shooting frothy seawater onto the streets.
The storm is moving inland at a speed of 6 miles per hour and conditions are likely to deteriorate as it pushes its way southwest along the coast Friday through Saturday. The experts managed to film the center of Florence as it makes its way toward the east coast, igniting evacuations all across the Carolinas, Virginia and DC.
The Weather Channel has been using mixed reality to great effect with its reporting on Hurricane Florence, showing how the water may rise and swallow buildings and cars in its path.