The viral video, which has more than 13.6 million views, showed Weather Channel correspondent Mike Seidel in Wilmington, North Carolina, trying to fight the heavy wind as he reported live from the storm on Friday.
Coastal streets flowed with ocean water, and more than 460,000 homes and businesses were without power, mostly in North Carolina, according to poweroutage.us, which tracks the nation's electrical grid.
In New Bern, North Carolina, the storm surge overwhelmed the town of 30,000, located at the confluence of the Neuse and Trent rivers.
As the storm lashed North and South Carolina Friday as a hurricane, FEMA officials warned of the storm's menacing rain.
"This storm is going to continue its violent grind across our state for days", Cooper said.
Officials in New Bern, which dates to the early 18th century, said more than 100 people were rescued from floods and the downtown was under water by Friday afternoon. It was downgraded to a Category 1 hurricane before coming ashore near Wrightsville Beach close to Wilmington, North Carolina.
"The cost to SC, if that happens, if the storm continues the way it is going, could be in the billions", Dahler said.
The National Hurricane Center said Florence is expected to be re-categorised as a tropical depression by the time it moves into the mid-Atlantic states and New England in the middle of next week. The coming storm surges and heavy rains will cause severe flooding that may submerge parts of the Carolinas in up to 40 inches of rain.
It remains a Category 1 hurricane with top sustained winds of 90 miles per hour (150 kph), but a gust of 112 miles per hour (180 kph) was reported just offshore.
The Miami-based center says Florence is bringing "catastrophic" fresh water flooding over a wide area of the Carolinas.
Forecasters say "it can not be emphasized enough that the most serious hazard associated with slow-moving Florence is extremely heavy rainfall, which will cause disastrous flooding that will be spreading inland".
Florence could become a major test for the Federal Emergency Management Agency, which was heavily criticized as slow and unprepared previous year for Hurricane Maria in Puerto Rico, where the death toll was put at almost 3,000.
"Honestly, I'm not sure" why some people refused to follow evacuation orders, David Cotton, county manager for North Carolina's Onslow County, told "Good Morning America" on Saturday.
North Carolina alone is forecast to get 36 trillion litres, enough to cover the Tar Heel state to a depth of about 25 centimetres.
The wind howled and sheets of rain splattered against windows of a hotel before dawn in Wilmington, where Sandie Orsa of Wilmington sat in a lobby lit by emergency lights after the power failed.
"We have also gotten calls from family members anxious about relatives they can't reach".
Fearless volunteers are seen defying the danger and continuing to rescue residents and their pets. "We got thrown into mailboxes, houses, trees", said Holt, who had stayed at home because of a doctor's appointment that was later canceled. She was eventually rescued by a boat crew; 140 more awaited assistance.
Ashley Warren and boyfriend Chris Smith managed to paddle away from their home in a boat with their two dogs, and were left shaken.