Florence's top sustained winds remain at 70 miles per hour (110 kph) as it crawls west at just 3 miles per hour (6 kph).
Heavy rainfall could leave nearly all of North Carolina in several feet of water, it's feared.
Atlantic Beach on North Carolina's Outer Banks islands had already received 30 inches of rain, the US Geological Survey said, while more than 25 inches have fallen in the Newport, Morehead City area since Thursday.
North Carolina's Harnett County declared a mandatory evacuation on Saturday along the Lower Little River, which is expected to rise to more than 17 feet above flood stage.
He said "24 to 36 hours remain for significant threats" from heavy rain, storm surge and flooding.
- A husband and wife died in a Fayetteville, North Carolina house fire on Friday, the state's Office of the Chief Medical Examiner says.
"I'll tell you, this one is so widespread, you're going to have a hard time finding a North Carolinian who is not going to be affected by this storm in some way", Cooper said.
The governor said half a million people in North Carolina were without power and the Neuse River had seen storm surge as high as 10 feet.
- A mother and her 8-month-old child were killed when a massive tree crushed their brick house Friday, according to a tweet from Wilmington, North Carolina police.
A fourth person reportedly was killed while plugging in a generator in the state's Lenoir County, according to U.S. media.
More than 12,000 people were in shelters in North Carolina and 400 in Virginia, where the forecast was less dire.
Airlines canceled more than 2,100 flights through Sunday.
With flood waters rising rapidly in many communities, stranded people were being rescued by boat and by helicopter, while tens of thousands of others hunkered down in shelters.
"Once these winds start blowing at that tropical storm rate it would be virtually impossible for the rescuers to get in to rescue you", Gov. Henry McMaster warned. "I feel like the dumbest human being who ever walked the face of the earth".
"If you could get to a second level somewhere, you might - you might have a chance to be able survive this level of storm surge flooding".
More than 1.7 million people in Virginia, North and SC were told to evacuate ahead of Florence's arrival.
North Carolina Governor Roy Cooper has urged residents in the path of the storm to "stay in a sheltered place" as Florence will "continue its violent grind across the state for days".
New Bern Mayor Dana Outlaw said in an interview with The Charlotte Observer around 5 a.m. that about 200 people had been rescued so far.
Rescued families were delivered to shelters, where approximately 20,000 people across the state were housed on Saturday.
The program was used in North Carolina after Hurricane Matthew in October 2016.
"Our house is on high ground so we're not anxious about the flooding", he said.
Myrtle Beach, a SC beach resort, was deserted with empty streets, boarded up storefronts and very little traffic.
Antonio Ramirez, a construction worker from El Salvador living in Leland, North Carolina, said he planned to ride out the worst of the weather with his dog Canelo.
Tom Balance, owner of a seafood restaurant in New Bern, had decided against evacuating his home and was soon alarmed to see waves coming off the Neuse and the water getting higher and higher.
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