At least 17 people have died in North and SC, as rescuers in pulled residents from homes threatened by swollen rivers.
At least 18 people were killed in the storm.
"What we are the most concerned about is, we have five major rivers that surround us, and we only have one major road into Myrtle Beach, but all of our major roads are going to be affected by this flooding within the next three to seven days", she said.
The coastal city of Wilmington, North Carolina, remained cut off by flood waters early on Monday.
"We're seeing this happen now and the result is not good", Cooper said.
Florence, which came ashore as a hurricane on Thursday before weakening to a tropical depression by Sunday, is expected to weaken again today before re-intensifying on Tuesday and Wednesday, the US National Hurricane Center said.
So far, the storm has claimed at least 17 lives.
Kaiden's mom, who has not been named publicly, was driving along North Carolina Highway 218 on Sunday when they encountered a barricade across the roadway, the office said.
North Carolina Governor Roy Cooper has urged residents who were evacuated from the worst-hit areas ahead of Hurricane Florence to stay away amid warnings that the floods in the state were worsening.
The area, about 100 miles from the North Carolina coast, includes part of the city of Fayetteville.More news: Dena Bank, Vijaya Bank and Bank of Baroda to be merged
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As all of the rain in the area entered the river system, the Lumber River reached a startling high of 25 feet on Sunday - about 12 feet about flood stage. More than 60 percent of homes and businesses were without power, and crews have completed about 700 rescues in the county where Wilmington is located.
The number of customers without power across North Carolina fell to just under 500,000, with about 20,000 in SC.
Experts say people likely got complacent about Florence because of a scale that only categorizes hurricanes by wind strength.
Rescuers freed six dogs that were locked up in an outdoor cage in North Carolina during Hurricane Florence, as the water level was rapidly rising.
Flooding worries also increased in Virginia, where roads were closed and power outages were on the rise.
"I lost everything in the flooding", he said.
"Flood waters are rising as rivers crest and they will for days".
Tens of thousands of houses have been damaged, but for many parts of the Carolinas, "the worst is yet to come" as river levels rise to historic levels, said Zach Taylor, a meteorologist with the US National Weather Service.
Local artist Kevin Bryant praised the effort, saying "it's good to get some support".
An 88-year-old man was also found dead in Union County on Monday, next to a auto that had been submerged in the floods.
Large segments of the major corridor also were closed in North Carolina, making north-south travel subject to long detours.