North Carolina Governor Roy Cooper told reporters that five deaths have been officially confirmed in his state, with several more under investigation.
The figure included a woman and her baby killed when a tree fell on their house.
Florence made landfall Friday as a Category 1 hurricane but has since been downgraded to a tropical storm, even as it continued to wreak havoc along the East Coast, downing trees and power lines and forcing 20,000 people to flee to shelters.
On Saturday some residents tried to return to home, driving through flooded highways armed with chainsaws to clear fallen pine needle trees that covered the road.
Cooper said others should not follow suit.
“Many people who think the storm has missed them have yet to see its threat,” he said, adding: “Don’t go back until this storm passes and you get the official all clear.
“Know that water is rising fast everywhere, even in places that don’t typically flood. This system is unloading epic amounts of rainfall: in some places, measured in feet, not inches.”
In a separate briefing, Steve Goldstein of the National Oceanic and Atmospheric Administration (NOAA) said some areas have already received two feet of rain and could expect up to 20 inches more as the system moved “slowly, nearly stationary” over eastern North Carolina.
In New Bern, a riverfront city near the North Carolina coast that saw storm surges up to 10 feet (3 meters), authorities were rescuing stranded residents and taking stock of damages.
“Right now we’ve rescued over 400 people. We still have about 100 that want to be rescued and we have about 1,200 in the shelters,” Mayor Dana Outlaw told CNN.
“We have 4,200 damaged homes,” he said, urging residents to not wade out into the streets because of the dangers posed by downed power lines.
The doors of many homes suffered so much wind damage they appeared to have been kicked in, while the city’s beloved fiber-glass bear statues, which are sponsored by local businesses, were floating down streets.
In one piece of good news authorities said that 16 wild ponies of hurricane-struck Ocracoke Island, located off the North Carolina coast, were safe.
The mother and her baby were killed in New Hanover County when a tree fell on their house, North Carolina Governor Roy Cooper told media late Friday.
Firefighters said the area had not been in the zone under evacuation orders.
Local authorities reported a death in Pender County when downed trees prevented emergency units from reaching a woman with a medical condition. Local media said she suffered a heart attack.
US media later said a man in Lenoir County died after heavy winds knocked him down as he tried to check on his dogs.
More than 800,000 customers in North Carolina were without power and 21,000 people were being housed in 157 shelters across the state.
The White House said President Donald Trump would visit hurricane-hit areas next week “once it is determined his travel will not disrupt any rescue or recovery efforts.”
As of 2:00 pm (1800 GMT), maximum sustained winds had weakened to near 45 miles (75 kilometers) per hour, but the NHC warned residents of dangerous storm surges and “catastrophic flooding.”
The military announced Saturday it was deploying nearly 200 soldiers to assist in storm-related response and recovery efforts, along with 100 trucks and equipment.
Besides federal and state emergency crews, rescuers were being helped by volunteers from the “Cajun Navy” – civilians equipped with light boats, canoes and air mattresses – who also turned up in Houston during Hurricane Harvey to carry out water rescues.
Hurricane Florence made landfall Friday in Wrightsville Beach, North Carolina, after stalking the coastline for days.
Tornadoes remain a threat, with the NHC saying that “a few tornadoes are possible in southeastern North Carolina and northeastern South Carolina.”
About 1.7 million people in North Carolina, South Carolina and Virginia are under voluntary or mandatory evacuation orders, and millions of others live in areas likely to be affected by the storm.