The death toll rose to at least 16.
As of Saturday, about 676,000 homes and businesses were without power in North Carolina, along with 119,000 in SC. 'And numerous rivers will see prolonged flooding, some not cresting for a few days'.
"(A) reas of the North Carolina Piedmont and the mountainous terrain of western North Carolina will experience devastating flash flooding unlike anything in recent memory", tweeted Greg Carbin, chief of the operations branch at the National Weather Service.
More than 800,000 customers in North Carolina were without power and 21,000 people were being housed in 157 shelters across the state.
As rivers swelled, state regulators and environmental groups were monitoring the threat from big hog and poultry farms located in low-lying, flood-prone areas.
"I have never seen flash flooding like this in our state", said state North Carolina Transport Secretary Jim Trogdon.
"As the storm begins to finally recede, they will kick into an even higher gear. We continue to patrol the area, but people have already been through Matthew hurricane and know what to expect", he told AFP.
Thousands of people living within a mile of part of the Cape Fear River and Little River have been ordered to leave their homes.
Woody White is chairman of the board of commissioners of New Hanover County. "We want you home, but you can't come yet".
Resident Joseph Eudi looks at flood debris and storm damage from Hurricane Florence at a home on East Front Street in New Bern, N.C., Saturday, Sept. 15, 2018.
Anne Francis Coronado came back on Sunday to inspect the damage with her husband.
"Amazing. They did awesome", Kevin Knox said.
On a flooded road near New Bern, Bryan Moore and his nephew Logan made a decision to go swimming in the floodwaters after having spent days at home without electricity or running water.
"If not we'd be stuck upstairs for the next ... how long? We're just having a good old time out here, enjoying the weather".
Hundreds of water rescues have been carried out by local authorities, the Cajun Navy volunteers and the U.S. Coast Guard since Friday morning. State Transportation Secretary Jim Trogdon said one of his top priorities was determining how to restore ground access to the area. "Don't make yourself someone who needs to be rescued".
Total accumulated rainfall there could end up as high as 40 inches.
The Carolinas' swollen rivers were beginning to swamp coal ash dumps and low-lying hog farms, raising concerns about water pollution.
At least 10 people have died so far in the storm in North Carolina, including a mother and child killed by a falling tree, state officials said.
By Sunday morning the storm's winds had dropped to about 35 miles per hour (55 km per hour), the National Hurricane Center in Miami said.
It was expected to accelerate to the north on Sunday night and then turn eastward across southern New England on Tuesday.
Donald Trump said federal emergency workers, first responders and law enforcement officials were "working really hard" in the extreme weather.