The eye of the storm and its outer edges pushed a life-threatening storm surge of floodwater miles inland and ripped apart buildings with screaming wind and pelting rain.
As 400-mile-wide Florence pounded away at the coast with torrential downpours and surging seas, rescue crews used boats to reach scores of people besieged by rising waters along a river.
Volvo closed its new plant in Charleston, South Carolina, which employs 1,000 people who make the company's S60 sedan. "You may need to move up to the second story, or to your attic, but WE ARE COMING TO GET YOU".
Coastal streets in the Carolinas flowed with frothy ocean water, and at least 510,000 homes and businesses were without power, almost all of them in North Carolina, according to poweroutage.us, which tracks the nation's electrical grid.
More than 634,000 homes and businesses were without power in North and SC early on Friday, utility officials said.
One resident, 67-year-old Linda Smith, told the MailOnline: "We're a little anxious about the storm surge so we came down to see what the river is doing now".
The NHC said the threat of tornadoes was increasing as Florence neared shore and South Carolina Governor Henry McMaster said the heavy rain could trigger landslides in the west of his state.
The station reported the fourth death involved a 77-year-old Kinston man who family members said died at 8 a.m. Friday when he was "blown down by the wind" while tending dogs. Florence is expected to arrive in southeast North Carolina on Friday morning before drifting south into SC.
And while Florence was downgraded to a tropical storm Friday afternoon, meteorologists predict heavy rain - up to 2 feet of rain when all is said and done - will continue into the weekend.
And about 46 miles (74 kilometres) farther up the waterfront, in New Bern, about 150 people were waiting to be rescued from floods on the Neuse River, WXII-TV reported.
More than 60 people, including many children and pets, were evacuated from a hotel in Jacksonville, North Carolina, after strong winds caused parts of the roof to collapse, local officials said.
"We already bought candles, batteries, can food items, water and so on".
"There is still time, but not a lot of time", said Derrec Becker of the South Carolina Department of Emergency Management.
The father sustained injuries and was transported to New Hanover Regional Medical Center in Wilmington for medical care. "And since we're already on high ground, those two things together kind of help insulate us a little more than, I would say, others".
North Carolina corrections officials said more than 3000 people were relocated from adult prisons and juvenile centres in the path of Florence, and more than 300 county prisoners were transferred to state facilities.
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