Florence was one of two major storms threatening millions of people on opposite sides of the world.
A mother and her baby died when a tree fell on their home in Wilmington, North Carolina.
The father of the child, who was also in the house, was transported to the New Hanover Regional Medical Center with injuries, police added, without releasing the names of the casualties. The southeast part of the state is expected to get more than twice that amount in the days ahead, said Bryce Link, a meteorologist at DTN Marine Weather, a forecasting service.
Soon afterwards, the administration of North Carolina Governor Roy Cooper said that a 78-year-old man died of electrocution as he was attempting to connect a power generator, while media reported that a 77-year-old man was killed after a gust of wind knocked him to the ground.
The biggest threat brought by Florence, which has been downgraded to a Category 1 storm, is not wind but water.
The enormous storm crept at a 6 miles per hour pace, making it clear that the trouble was just beginning.
Coast Guard helicopters were taking off across the street to rescue stranded people from rooftops and swamped cars.
Boat teams rescued residents Sadie Marie Holt, 67, who first tried to row out of her neighborhood during Florence's assault. Additionally, three people have died in SC. "Sixty mile-per-hour winds, shingles flying off their own homes, and they're here working for everyone else". By late afternoon, Beaufort County Manager Brian Alligood hoped the worst was over.
The hurricane was seen as a major test for the Federal Emergency Management Agency, which was heavily criticized as slow and unprepared for Hurricane Maria in Puerto Rico previous year. "That is a lot of rain and all that rain runs off into the rivers and we've been talking about this - there is elevation as you get further west into North Carolina".
This satellite image provided by NOAA shows Hurricane Florence on the eastern coast of the United States. Image AAP
Cruise ships have diverted to Florida away from the storm's path, and some hotels are offering special discounts for evacuees.
Lisa Evers and her daughter, Amanda Hamilton, decorate their storm shutters before leaving their home ahead of Hurricane Florence in Oak Island, N.C.
The city of Jacksonville's statement says people have been moved to the city's public safety center as officials work to find a more permanent shelter.
Rain ranging from one to three and a half feet has already fallen, and it's not over.
Power outages increased throughout Friday. Airlines canceled more than 2,400 flights through Sunday.
Numerous roads were closed, and authorities warned of the risk of landslides, tornadoes and flash floods, with dams and bridges in peril as rivers and creeks swelled.
Tropical Storm Florence is practically stalled over the Carolinas and the monster storm could dump drenching rains of up to 3½ feet (1 meter). Residents mostly heeded police commands to stay home and off the streets. But once New Bern TV news station WCTI evacuated its newsroom Thursday night because of flooding and people began to lose power, the seriousness of the situation began dawning on folks, she said.
"It's an uninvited brute who doesn't want to leave". Rainfall totals will depend on the speed of the storm, he said. Flooding also hit the Bogue Sound near Beaufort, the Pungo River at Belhaven and the Pamlico River at Washington.
Emergency crews were stretched thin.More news: NOAA: Sub-Tropical Storm Joyce Projected Path, Spaghetti Models
More news: US Open victor overtakes Swiss great
More news: Spurs duo Lloris, Alli to miss Liverpool, Inter clashes