At least five people have died since the storm crashed into the coast and almost stalled.
At the coast, the (Raleigh) News & Observer reported that hundreds of people were rescued or awaiting rescue as the Neuse River rose and flooded parts of New Bern. "I was born and raised here and been through every storm the last 30 years, but this one seems to be doing more damage than we expected".
More than 60 people meanwhile were forced to evacuate a hotel in Jacksonville, North Carolina, after part of the roof collapsed, city officials said.
A mother and child died in Wilmington when a tree fell on their home, police tweeted.
Shaken after seeing waves crashing in the Neuse River just outside his house in the town of New Bern, hurricane veteran Tom Ballance wished he had evacuated.
Still, he said: "I feel like the dumbest human being who ever walked the face of the earth".
The storm was downgraded late Thursday to a Category 1, as the North Carolina coast was battered by hurricane-force winds and a life-threatening storm surge. The last Category 4 storm to come out of the Atlantic and strike the North Carolina coast head-on was Hazel in 1954, the most destructive previous event in that region.
In the besieged North Carolina city of New Bern, rescuers by midmorning Friday had plucked more than 200 people from rising waters, but about 150 more had to wait as conditions worsened and a storm surge reached 10 feet, officials said.
But it was clear that this was really about the water, not the wind.
The Charlotte area is expected to see heavy rain and 30-40 miles per hour winds in the coming days, which could cause power outages and flooding in certain areas. Some areas of North Carolina saw nearly a foot of rain in just a few hours.
Debris from Hurricane Florence covers a street in downtown New Bern, North Carolina. Authorities warned, too, of the threat of mudslides and the risk of environmental havoc from floodwaters washing over industrial waste sites and hog farms.
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And just weeks after Hurricane Lane led to major floods in Hawaii, Hurricane Olivia could hit the state as early as Tuesday. The storm's first effects were already being seen Monday on barrier islands as risky rip currents hit beaches.
The US National Hurricane Center described how winds of up to 90 miles (150 kilometers) per hour were pummeling the state of North Carolina.
The worst of the storm's fury had yet to reach coastal SC, where emergency managers said people could still leave flood-prone areas. That's enough to fill the Chesapeake Bay, he calculated. "Nothing's hit the house yet, but it's still blowing". Moreover, the Carolinas have not seen such a storm since the 1980s.
On Friday, coastal streets in the Carolinas flowed with frothy ocean water, and pieces of torn-apart buildings flew through the air.
The NWS reported "lots of tree damage, debris and power lines down" across Harkers Island, N.C.
A wind gust at the Wilmington airport was clocked at 105 miles per hour, the highest since Hurricane Helene in 1958.
Airlines cancelled more than 2,100 flights through Sunday.
The powerful Atlantic storm began battering the Carolinas with rain, wind and floodwater.
Forecasters say it is especially risky after dark because people trying to escape may not realize how deep flood water is on roads.
"You can't get over till we have power and we have sewer up and running", said the retired teacher and real estate agent, who rode out the hurricane in an inland hotel.
"We've removed anything that has the potential to blow around", said deputy aviation director Jack Christine.
Between downed trees and rising water levels, some major roads were impassable and more secondary roads were also cut off.
People have left homes and taken precautions ahead of the hurricane.