"More significant weakening is forecast on Saturday as Florence moves farther inland over central SC", the NHC said on Thursday.
About 9,700 National Guard troops and civilians have been deployed, with high-water vehicles, helicopters and boats.
In less than 24 hours, Florence has dropped from category 4 to category 2.
Onslow County spokesman Cornelius Jordan said some visitors at the Triangle Motor Inn were able to drive away on their own, but emergency personnel had to take others to a safe location.
People in areas vulnerable to the unsafe hurricane, particularly those in coastal regions, have fled ahead of the storm.
The storm's first casualties, which included a mother and her baby killed when a tree fell on their brick house in Wilmington, North Carolina, were announced about eight hours after Florence came ashore.
Meteorologist Ryan Maue of weathermodels.com said Florence could dump a staggering 18 trillion gallons of rain over a week on North Carolina, South Carolinas, Virginia, Georgia, Tennessee, Kentucky and Maryland.
Hundreds of thousands of people in the Carolinas and Virginia have been forced to evacuate as Hurricane Florence battered the eastern coast of the USA, including more than 3,000 prisoners who have been relocated from jails in the path of Florence.
More than 80,000 people were already without power as the storm approached, and more than 12,000 were in shelters.
"In a matter of seconds, my house was flooded up to the waist, and now it is to the chest", said Peggy Perry, who along with three relatives, was trapped early Friday in her New Bern home, according to CNN.
Hurricane Florence weakened into a Category 2 hurricane as it moved towards east coast of the United States, the U.S. National Hurricane Center (NHC) said on Wednesday, but a life-threatening storm surge and heavy rainfall were still expected.
More than 722,000 homes and businesses were without power in North and SC early on Friday, utility officials said. Hundreds more were rescued elsewhere from rising water.
Sheets of rain splattered against windows of a hotel before daybreak in Wilmington, where Sandie Orsa of Wilmington sat in a lobby lit by emergency lights after the power failed.
Authorities said more than 60 people, including many children and pets, had to be evacuated from a hotel in Jacksonville, North Carolina, after strong winds caused parts of the roof to collapse.
"(It's) very eerie, the wind howling, the rain blowing sideways, debris flying", said Sandie Orsa, of Wilmington, who fears splintering trees will destroy her home.
Another 400 people were in shelters in Virginia, where forecasts were less dire. What's more, Florence's historic amount of rainfall may lead to flooding of pig manure lagoons, and the hurricane's winds and storm surge have the potential to damage nuclear reactors in the region, Live Science previously reported.
More than 1 million people have been ordered to evacuate the coastlines of the Carolinas and Virginia.
The path of Hurricane Florence sees it going over some of the poorest areas on the eastern seaboard.
Hurricane Irma destroyed Kathy Griffin's house in Florida past year, and it could be days before she finds out whether Florence smashed her fifth-story condominium in Wrightsville Beach, where authorities said utilities could be out for days or weeks.