Florence's intensity has diminished since it roared ashore along the US mid-Atlantic coast on Friday as a hurricane. But its slow march over the two states, crawling west at only 2 miles per hour (3 km per hour), is expected to leave large parts of the region deluged in the coming days.
"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. His state has already endured record rainfall, with much more forecast to come. Rivers will continue to rise days after the rain has stopped, he said.
"This is a hurricane event followed by a flood event," said South Carolina Governor Henry McMaster.
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. As of Saturday, about 676,000 homes and businesses were without power in North Carolina, along with 119,000 in South Carolina.
North Carolina officials said there had been at least seven storm-related fatalities in the state, with unconfirmed reports of a further three deaths. South Carolina authorities reported one death.
The White House said President Donald Trump approved making federal funding available in some affected counties. Trump, who plans a visit to the region next week, tweeted his "deepest sympathies and warmth" to the families and friends of those who had lost their lives.
WORST YET TO COME
At 8 pm EDT (0000 GMT), the National Hurricane Center said Florence had maximum sustained winds near 45 miles per hour, and was slowly drifting westward over South Carolina.
The center said the storm would dump as much as 40 inches (102 cm) of rain along coastal areas of the Carolinas, as well as up to 10 inches in southwestern Virginia.
In Fayetteville, a North Carolina city of about 210,000 people about 90 miles inland, authorities told thousands of residents near the Cape Fear River and Little River to get out of their homes by Sunday afternoon because of the flood risk.
"The worst is yet to come," he added.
The storm made landfall on Friday near Wilmington, a city of about 120,000 squeezed between North Carolina's Atlantic coastline and the Cape Fear River. On Saturday, its streets were strewn with downed tree limbs and carpeted with leaves and other debris. Electricity remained out for much of the city, known for its historic mansions, with power lines lying across roads like wet strands of spaghetti.
"The fact that there haven't been more deaths and damage is amazing and a blessing," said Rebekah Roth, walking around Wilmington's Winoca Terrace neighbourhood.
Near the Sutton Power Plant in Wilmington, coal ash leaked from a Duke Energy landfill. The site lost enough material to fill around two-thirds of an Olympic-sized pool, the company said in a statement, adding that it did not believe the incident posed a risk to health or the environment.
Officials had warned before the storm that the rains could risk tainting waterways with murky coal ash and toxic hog waste.
In New Bern, about 90 miles northeast of Wilmington at the confluence of two rivers, Florence overwhelmed the town of 30,000 and left the downtown area under water. Some area residents described a harrowing retreat as the storm hit.
"It was pitch black and I was just scared out of my mind," said Tracy Singleton, who with her family later drove through torrential rain and high winds from her home near New Bern.
South Carolina authorities said law enforcement officers were guarding against looting in evacuated areas, while Wilmington set a curfew on Saturday evening in response to looting in one area.
As the United States dealt with Florence, a strong typhoon tore across the northern tip of the Philippines, wrecking homes and triggering landslides before heading toward Hong Kong and China.