Life-threatening, catastrophic flash floods and prolonged significant river flooding are possible in portions of North Carolina, South Carolina and the southern to central Appalachias to western North Carolina to west-central Virginia and far-eastern West Virginia into early next week, the National Weather Service said.
A mother and her baby lost their lives after a giant tree collapsed.
More than 1 million people, mainly in North Carolina, were without power a day after Florence made landfall a few miles east of Wilmington as a howling Category 1 hurricane.
The White House said President Trump had issued a disaster declaration for North Carolina a day earlier, freeing up funds for housing and home fix.
In one piece of good news, authorities said 16 wild ponies of hurricane-struck Ocracoke Island, located off the North Carolina coast, were safe.
"Know that water is rising fast everywhere, even in places that don't typically flood". "This system is unloading epic amounts of rainfall".
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.
In New Bern, along the coast, homes were completely surrounded by water, and rescuers used inflatable boats to reach people.
None of the people rescued were injured.
In its initial onslaught along the coast, Florence buckled buildings, deluged entire communities and knocked out power to more than 900,000 homes and businesses in NC.
If Florence doesn't wipe out oceanfront homes on stilts along the Carolinas coast, rising sea levels will. Florence lashed low-lying barrier islands that experience some of the fastest rates of sea level rise observed anywhere in the world, almost an inch (2.5 centimeters) a year.
Officials in New Bern, a town dating to the early 18th century whose downtown area was under water, said more than 100 people were rescued from floods on Friday, with 60 to 75 people awaiting rescue on Saturday. The evacuation zone included part of the city of Fayetteville, which has a population 200,000. Local media said she suffered a heart attack. A 78-year-old man connecting extension cords in the rain was electrocuted, according to Roger Dail, the Lenoir County director of emergency services.
As rains inundate North Carolina due to Tropical Storm Florence, the state Department of Transportation is warning residents about rapidly deteriorating road conditions due to downed trees and flooding.
"This is a hurricane event followed by a flood event", said South Carolina Governor Henry McMaster.
The White House said Trump would visit hurricane-hit areas next week 'once it is determined his travel will not disrupt any rescue or recovery efforts'.
Boat teams including volunteers rescued some 360 residents, including Sadie Marie Holt, 67, who first tried to row out of her neighborhood during Florence's assault.
And dolphins were spotted closer than usual to shore near in Wilmington, North Carolina.
North Carolina alone is forecast to get 9.6 trillion gallons (36 trillion liters), enough to cover the Tar Heel state to a depth of about 10 inches (25 centimeters).