It already had, in Beaufort County and its capital city, Washington, where 300 people were rescued from flooded homes.
As it moves inland, the storm is expected to bring its high winds and intense rain bands across the southeastern corner of North Carolina and a large chunk of SC.
Video shows a woman in a pink raincoat carrying her rottweiler above the rising waters in New Bern, North Carolina.
More than 60 people had to be rescued in another town as a cinderblock motel collapsed at the height of the storm's fury.
Florence flattened trees, crumbled roads and knocked out power to more than 700,000 homes and businesses, and the assault wasn't near an end.
The worst of the storm's fury had yet to reach coastal SC, where emergency managers said people could still leave flood-prone areas.
Mr Cooper said the hurricane was "wreaking havoc" on the coast and could wipe out entire communities as it makes its "violent grind across our state for days".
In one incident, a mother, 41, and her 7-month-old son were killed when a tree fell on their house in Wilmington.
Still, he said: "I feel like the dumbest human being who ever walked the face of the earth".
Florence made landfall as a Category 1 hurricane at 7.15 am at Wrightsville Beach, a few miles east of Wilmington and not far from the SC line, coming ashore along a mostly boarded-up, emptied-out stretch of coastline.
By Friday evening, the centre of the storm had moved to eastern SC, with maximum sustained winds of 70 miles per hour. "Lots of water, lots of wind, lots of storm surge".
Florence's storm surge and the prospect of 1 to 3½ feet of rain were considered a bigger threat than its winds, which dropped off from an alarming 140 miles per hour earlier in the week.
The river swamped the town after Hurricane Matthew came through two years ago: One church parishioner drowned during that storm, more than 700 families were displaced from their homes, and two of the city's largest public housing projects were destroyed, Foreman said.
Forecasters have been predicting catastrophic flash flooding.
Preparing for the worst, about 9,700 National Guard troops and civilians were deployed with high-water vehicles, helicopters and boats that could be used to pluck people from the floodwaters.
Authorities warned, too, of the threat of mudslides and the risk of an environmental disaster from floodwaters washing over industrial waste sites and hog farms.
"A USGS gauge in Emerald Isle, N.C., recently recorded 6.1 feet above normal water levels", the National Hurricane Center said of the storm surge early Friday.
The National Hurricane Center said Florence will eventually make a right hook to the northeast over the southern Appalachians, moving into the mid-Atlantic states and New England as a tropical depression by the middle of next week.
About 10 million people could be affected by the storm and more than 1 million were ordered to evacuate the coasts of the Carolinas and Virginia. That's enough to fill the Chesapeake Bay or cover the entire state of Texas with almost 10cm of water, he calculated. EMS services could not get to the woman due to the storm, marking the third Florence-related death since the storm began hitting the North Carolina coastline.
Pieces of torn-apart buildings flew through the air.
Airlines canceled more than 2,100 flights through Sunday. They believe he died after going outside to check on his hunting dogs and was blown down by the wind. The Neuse River rose rapidly, overcoming the streets of New Bern. "Nothing you need to get a chain saw after yet", he said by phone.
He said "24 to 36 hours remain for significant threats" from heavy rain, storm surge and flooding. "It's very hard to say at this point".
"Some of the rainfall totals we're getting are already adding up to about 14 inches", NHC Director Ken Graham said shortly after 11 a.m. ET.
As she sat in the hotel lobby eating a cold breakfast of bananas, cereal bars, and pastries, she recalled that the decision to heed the mandatory evacuation order for her area wasn't hard.
"Honestly, I grew up in Wilmington".
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