"If the river rises to the level they say it's going to, then this warehouse is going to be under water".
Cutting off the coastal city of Wilmington, damaging tens of thousands of homes and filling river to bursting point, the storm has wreaked extensive damage on both North and SC despite rapid weakening.
"I have never seen flash flooding like this in our state", said state North Carolina Transport Secretary Jim Trogdon.
The storm was downgraded to a tropical depression as it trudged inland early yesterday morning, knocking out power and causing at least eight deaths as flood waters kept rising.
About 756,000 homes and businesses were without power in North and SC and surrounding states, down from a peak of almost 1 million.
"This is still a catastrophic, life threatening storm", said Zack Taylor, a meteorologist with the US National Weather Service's Weather Prediction Center.
That's the new North Carolina record for most rainfall from a single tropical system.
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"We have 4,200 damaged homes", Mayor Dana Outlaw told CNN.
30-year-old Rhonda R. Hartley died early Sunday after driving a pickup truck into standing water near Gilbert, South Carolina, losing control and hitting a tree, according to the South Carolina Department of Public Safety.
More than 900 people were rescued from rising floodwaters and 15,000 remained in shelters in the state, Cooper said.
"As the storm begins to finally recede, they will kick into an even higher gear".
In the Lehigh Valley, Davis said the rainfall could result in some localized flash flooding and wind gusts of about 20 miles per hour, much less than the over 105 miles per hour gusts Thursday night that sent seawater surging ashore along the Outer Banks in North Carolina. "We continue to patrol the area, but people have already been through Matthew hurricane and know what to expect", he told AFP. "The risk is growing as well in the mountains, where rains could lead to risky landslides", he said.
The centre of the storm was just west of Raleigh, the state capital, and moving north at 14 miles per hour (22 kph), the hurricane centre said.
The White House said President Donald Trump approved making federal funding available in some affected counties.
Additionally, a few tornadoes "remain possible" Sunday and Monday across North Carolina and eastern SC.