The storm was expected to move across parts of southeastern North Carolina and eastern SC on Friday and Saturday, then head north over the western Carolinas and central Appalachian Mountains early next week, the NHC said.
Forecasters and politicians pleaded with the public to take the warnings seriously and minced no words in describing the threat.
On Wednesday morning, the storm was about 550 miles from the Carolina coast and remains a Category 4 storm with 130 mph winds.
Once a Category 4 hurricane with winds of 140 miles per hour, the hurricane was downgraded to a Category 1 on Thursday night. "Don't bet your life on riding out a monster".
Governor Cooper said the state would arrange a visit by Trump "at an appropriate time".
It is unclear exactly how many people fled, but more than 1.7 million people in the Carolinas and Virginia were urged to evacuate. But getting out of harm's way could prove hard. Meanwhile, Dominion Energy, the major electric utility in Virginia and North Carolina, expects many of its customers to lose power from Florence's intense winds and persistent rain, which could linger for days over a wide swath of the mid-Atlantic region.
Residents prepared by boarding up their homes and stocking up on food, water and other essentials, stripping grocery store shelves of merchandise.
A line of heavy traffic moved away from the coast on Interstate 40, the main route between the port city of Wilmington and inland Raleigh. With that much size and strength, even a glancing blow could be devastating - something forecasters stressed as they noted the shift in the predicted track. Many gasoline stations were running low on fuel. "We've never seen anything quite like this, on the East Coast at least", he said, according to Reuters.
About 5.25 million people live in areas under hurricane warnings or watches, and 4.9 million in places covered by tropical storm warnings or watches, the National Weather Service said.
About 245,000 Virginians who live in the storm's path have been ordered to evacuate their homes, while more than 1 million in North Carolina and SC have been told to flee.
Florence had been a Category 3 hurricane with 120-mph winds on Thursday, but dropped to Category 1 before coming ashore. Officials met Wednesday to discuss plans and monitor the hurricane. "Stay on guard. This is a powerful storm that can kill". It's going to destroy infrastructure.
Communities could lose electricity for weeks, Federal Emergency Management Agency (FEMA) Administrator Brock Long said.
Some areas are expected to see between 20 and 30 inches of rain through early next week in the area shaded in purple in the second image above.
Weekend sporting events have already been canceled, with possibly more to come.
The result could be catastrophic inland flooding that could swamp homes, businesses, fields and industrial sites.
"These enormous waves are produced by being trapped along with very strong winds moving in the same direction [of] the storm's motion", the agency said.
About 10 million people could be affected by the storm.
Paula Matheson of Springfield, Oregon, got the full Southern experience during her 10-week RV vacation: hot weather, good food, attractive beaches and, finally, a hurricane evacuation.
With South Carolina's beach towns more in the bull's-eye because of the shifting forecast, OH tourists Chris and Nicole Roland put off their departure from North Myrtle Beach to get the maximum amount of time on the sand. The water was fabulous.
Florence's winds dropped from a peak of 140 miles per hour to 90 miles per hour on Thursday.