Pieces of torn-apart buildings flew through the air.
Florence's large wind field will add to the perils as the storm grinds over beaches and inland.
There were no immediate reports of storm-related deaths or serious injuries.
Florence was expected to make landfall near Cape Fear, North Carolina, at midday, and forecasters said its size meant it could batter the U.S. East Coast with hurricane-force winds for almost a full day.
According to CNN, the hurricane hit the east coast of the U.S. with 90-mph winds and relentless rain.
The Miami-based center had said earlier Friday Florence's arrival would come with "catastrophic" fresh water flooding over portions of the Carolinas. On the morning of September 14, the National Hurricane Centre warned that "catastrophic" flooding and "life-threatening" storm surges were expected to spread inland.
Ominously, forecasters said the onslaught on the North Carolina-South Carolina coast would last for hours and hours because the hurricane had come nearly to a dead stop at just 3 mph (6 kph) as of midday. The system is expected to bring its gusty winds, which extend some 140 miles from its center, and heavy rains to the Azores, according to the National Hurricane Center.
Forecasters said Florence's surge could cover all but a sliver of the Carolina coast under as much as 11 feet of sea water. "Nothing's hit the house yet, but it's still blowing".
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In New Bern, population 29,000, flooding on the Neuse River trapped people, and Mayor Dana Outlaw told The Charlotte Observer that about 200 had been rescued by 5 a.m. Residents reached out for help through the night by phone and social media.
FEMA teams were employing boats in the rescues and were determining which cases were the most severe.
"There is still time, but not a lot of time", said Derrec Becker of the South Carolina Department of Emergency Management.
A North Carolina city says about 70 people have been rescued from a hotel whose structural integrity is being threatened by Hurricane Florence.
More than 80,000 people in North Carolina already were without power as the storm began buffeting the coast, and more than 12,000 were in shelters.
The huge, slow-moving storm has caused many businesses in its path to close its doors, including a number of big automakers and retailers. Deadly storm surges, flooding and inland rainfall are expected to cause significant damage as well. Restoring power to all customers could take weeks, it said. "We've had it reported to where it's over mailboxes, to the stairs of homes, even at first, second floors to where people are having to get on their roofs".