Florence remains a Category 1 storm, and it's spinning hurricane-force winds up to 70 miles from its center.
Ken Graham, the NHC's director, warned the slow pace of the storm exacerbated its danger even to areas outside its immediate path.
The surge in power outages along the coast was the result of gusts coming off Hurricane Florence and blowing trees into power lines, said Lisa Crawley, a spokeswoman for the co-ops.
More than 400 people had to be rescued from their homes or vehicles and some 20,000 were taking refuge in shelters across North and SC and Virginia. In Craven County, authorities say they received more than 150 telephone calls to rescue people in the historic town of New Bern because water had entered their homes.
The No. 1 mission right now, Cooper said, is to save lives.
In New Bern, Sarah Risty-Davis is one of the residents who opted not to follow a mandatory evacuation order that was issued three days ago.
There's still a threat from rising tides, Risty-Davis says.
"The fact is this storm is deadly and we know we are days away from an ending", Cooper said.
Sample said that when he looked outside of his house, which is about 1,000 yards from the beach, he saw the rain pooling up on the street and what looked like storm surge coming up the road. The agency adds that people trapped by flooding should "never enter attics or crawl spaces".
"A big worry about Hurricane Florence is that it's not acting like a normal hurricane", said Al Jazeera's Andy Gallacher, reporting from Wilmington, North Carolina.
A wind gust at the Wilmington airport was clocked at almost 170km/h, the highest since Hurricane Helene in 1958.
To the south, storm surge pushed water levels at Johnny Mercer Pier at Wrightsville Beach, where Florence made landfall at 7:15 a.m. with 90 miles per hour winds, to more than 8.5 feet.
Meteorologists expect the storm to hover over the Carolinas through Saturday as it moves inland, rolling over parts of Georgia and Tennessee into Sunday afternoon and then weakening to heavy rain and wind in traveling up the Appalachians toward the Northeast.
"This rainfall will produce catastrophic flash flooding and prolonged significant river flooding", the hurricane center said.
Florence's rain will bring 40 inches to some parts of the Carolinas, forecasters said.