The father was pulled from the home and transported to a local hospital with injuries, police said.
A third person, a woman, died in Hampstead, NC, in Pender County.
Flash flooding killed three people in Duplin County, North Carolina, the sheriff's office there said.
Officials said people across Cumberland County are in danger of losing their lives. TV station WNCN said the 78-year-old victim and was "trying to connect two extension cords outside in the rain".
"This system is unloading epic amounts of rainfall, in some places measured in feet and not inches", North Carolina Governor Roy Cooper told a news briefing.
Horry County Chief Deputy Coroner Tamara Willard said 63-year-old Mark Carter King and 61-year-old Debra Collins Rion were killed by breathing in carbon monoxide. A husband and wife died in a storm-linked house fire, officials said, and an 81-year-old man died after falling while packing to evacuate.
"The storm has never been more unsafe than it is now", North Carolina's emergency management office said on Twitter, quoting Governor Roy Cooper.
The eye of Florence directly struck Wrightsville Beach, NC, early Friday.
However, officials fear the worst from Florence is yet to come.
Forecast of heavy downpour is expected in both South and North Carolina in the next few days, according to officials.
Authorities say the storm did not cause some other deaths that occurred during Florence in North Carolina: a woman who died of undetermined causes in a shelter, a woman who suffered a heart attack at home during the storm, and a couple whose apparent murder-suicide was investigated during hurricane conditions in Otway.
As the death toll from Florence mounted and hundreds of people were pulled from flooded homes, North Carolina is bracing for what could be the next stage of a still-unfolding disaster: widespread, catastrophic river flooding.
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A.M. Update: Prolonged rain will bring floods
North Carolina Governor Roy Cooper said the storm was posing an even greater risk of flooding than when it first made landfall. In the town of New Bern , homes were completely surrounded by water, and rescuers had to use inflatable boats to reach people.
Volunteers from all over North Carolina help rescue residents and their pets from their flooded homes during Hurricane Florence September 14, 2018 in New Bern, United States. A nuclear power plant in Brunswick, NC, shut down operations Friday.
More than 30 inches (75cm) of rain has fallen across North and SC since Friday, with tens of thousands of people evacuated from their homes. Newport, NC, "reported a rainfall total of nearly 24 inches as of midnight Saturday", the NHC said. SC is the second-highest insured state for flooding, with roughly 65 percent of properties in flood hazard areas insured. A turn toward the northwest with an increase in forward speed is expected today, followed by a turn toward the north and northeast with an additional increase in forward speed on Monday.
The National Weather Service's Advanced Hydrologic Prediction Service is predicting "Major Flooding", its most severe classification, from the Pungo River in Belhaven, NC, to the Trent River in Pollocksville, NC, as of early Saturday morning.
The states of Georgia, South Carolina, North Carolina, Virginia and Maryland, as well as Washington D.C., declared a state of emergency ahead of the storm.
The remainder of northern SC into western North Carolina and southwest Virginia could see 5 to 10 inches of rainfall, with some isolated areas seeing 15 inches.
As it moves near OH and West Virginia, it will become a remnant low.
Those waves were coming from the Neuse River, which is about 25 feet (8 meters) away, and downhill, from his house.
Air swirls in to fill the low pressure in the storm, sucking air in and upwards, reinforcing the low pressure.
Downgraded to a tropical depression overnight, Florence was still massive.
Hurricanes are violent storms that can bring devastation to coastal areas, threatening lives, homes and businesses. Around 3:30 p.m. Thursday, the electricity went out.
Florence weakened to a tropical depression early Sunday and was crawling west at just 8 miles per hour (13 kph).