North Carolina Governor Roy Cooper said the storm was posing an even greater risk of flooding than when it first made landfall.
Florence diminished from hurricane strength as it came ashore on Friday, but the large storm's slow progress across the two states could leave much of the region under water in the coming days, according to forecasters.
By 5 a.m., about 200 people had been rescued from flooded homes in New Bern, where the National Weather Service reported 10 feet of inundation.
Forecasters say the center of Hurricane Florence is hovering just inland near Cape Fear, North Carolina.
Wind gusts as high as 60 miles per hour were recorded in the Myrtle Beach area.
North Carolina utilities estimated that as many as 2.5 million state residents could be left without power, the state's Department of Public Safety said.
By storm's end, up to 40 inches of rain will have fallen in parts of North Carolina and far northeastern SC, the National Hurricane Center said.
Florence flattened trees, crumbled roads and knocked out power to more than 840,000 homes and businesses, and the assault wasn't anywhere close to being over, with the siege in the Carolinas expected to last all weekend. At least five deaths are connected to the storm.
He advised never to drive through still or moving water covering roadways - and not to return to hard-hit areas until given an official "all-clear".
"Please be safe and be smart and use your common sense", Cooper added.
Blowing ashore with howling 90 miles per hour (155 kph) winds, Hurricane Florence splintered buildings, trapped hundreds of people and swamped entire communities along the Carolina coast Friday in what could be just the opening act in a watery, two-part, slow-motion disaster.
Rising water forced a North Carolina TV station to evacuate its newsroom in the middle of Hurricane Florence coverage.
Strong winds and heavy rain continue to present a danger, and Florence is now being attributed to several deaths.
High winds and storm surge from Hurricane Florence hits Swansboro N.C., on September 14, 2018.
It has already claimed five victims, with a mother and her baby crushed by a tree in North Carolina. The child's father was transported to the hospital with injuries.
"Our hearts go out to the families of those who died in this storm", Cooper said in a statement. Paramedics trying to reach her were blocked by debris.
Video footage shot during the tropical storm shows what appears to be two dolphins swimming in the rising storm surge water.
The body of a 77-year-old man, also in Kinston, was found by his family at his home, and it is believed he died when he was blown down after going outside to check on his hunting dogs, Dail said.
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.
More than 100 people were rescued and up to 75 more were awaiting rescue on Saturday morning, according to a town official.
Downtown New Bern, on the Neuse River also is flooded.
Some local residents described a harrowing retreat as the storm hit early on Friday.
"Life-threatening, catastrophic flash floods and prolonged significant river flooding are likely over portions of the Carolinas and the southern to central Appalachians from western North Carolina into southwest Virginia through early next week".
The scenes of the damage out of North Carolina near the teen's home where he hears his town is partially submerged are hard to wrap his mind around. With rivers swelling toward record levels, thousands of people were ordered to evacuate for fear the next few days could bring the most destructive round of flooding in North Carolina history. SC authorities reported one death.
The White House said yesterday President Donald Trump had approved making federal funding available in some counties.