Officials warn of life-threatening storm surges in North and SC as the hurricane moves towards land with maximum sustained wind speeds of 90mph (150 km/h). Just north of Conway, about 665 people are without power.
The Miami-based center says Florence is bringing "catastrophic" fresh water flooding over a wide area of the Carolinas. "We have two boats and all our worldly possessions", said Susan Patchkofsky, who refused her family's pleas to evacuate and stayed at Emerald Isle with her husband.
None of the people rescued were injured.
As of 5 a.m., Florence was 25 miles (55 kilometers) east of Wilmington, North Carolina.
"This rainfall will produce catastrophic flash flooding and prolonged significant river flooding", the hurricane center said.
More than 1.7 million people in the Carolinas and Virginia were warned to evacuate over the past few days, and the homes of about 10 million were under watches or warnings for the hurricane or tropical storm conditions.
In a display of the early effects of the storm, one flood gauge on the Neuse River in New Bern, North Carolina, showed three meters of flooding, the NHC said. Forecasters predict that high tides could rise as much as 3 feet above normal into Saturday in the city and in Anne Arundel, Baltimore, Calvert and Harford counties. "The larger and the slower the storm is, the greater the threat and the impact-and we have that".
And in Wilmington, North Carolina, a steady rain began to fall as gusts of winds intensified, causing trees to sway and stoplights to flicker.
"The first bands are upon us", Gov. Roy Cooper said Thursday evening.
Some minor flooding was reported on the Outer Banks - barrier islands off the coast of North Carolina - and in some seaside coastal towns, as more than 110,000 power outages were reported statewide. Emerald Isle is about 84 miles (135 kilometers) north of Wilmington.
The National Hurricane Center forecasts that it could be centered over southwestern Pennsylvania by early Tuesday morning, potentially bringing more rain to Maryland and another surge of floodwaters down an already swollen Susquehanna River.
The outer bands of Hurricane Florence drenched the Carolinas on Thursday, flooding roads, gorging rivers and knocking out power in an ominous glimpse of the damage the storm could inflict when it makes landfall on Friday with millions of people in its path. Florence, though downgraded to a Category 2 storm on the five-step Saffir-Simpson scale, remained risky and unpredictable, the National Hurricane Center (NHC) said. For a Category 2 storm, that means sustained winds of 154-177 km/h (96-110 mph).