The storm was heading for the coast of the two states but heavy rain was also expected in Virginia to the north and Georgia to the south.
A tropical storm warning is in effect for north of Duck, NC, to Cape Charles Light, VA, and for Chesapeake Bay south of New Point Comfort.
"Bad things can happen when you're talking about a storm this size", Trump said Wednesday morning.
A high-definition video camera outside the space station captured stark and sobering views of Hurricane Florence, at that time a Category 4 storm.
"Just because the wind speed came down, the intensity of this storm came down to a Cat 2, please do not let your guard down", said Brock Long, the administrator of the Federal Emergency Management Agency (FEMA).
Florence weakened slightly to a Category 3 storm on a five-step scale but had maximum sustained winds of 125 miles per hour (201 km per hour) as of 2 p.m. EDT (1800 GMT), down from 130 mph earlier in the day. As of 5 a.m., its maximum wind speeds remain at 110 miles per hour as it started to ingest drier air, says FOX 13's meteorologist Tyler Eliasen, however, it also means Florence's wind field has grown larger.
"I don't care if this goes down to a Category 1".
As of 11 a.m. EDT, Florence was centered about 145 miles (230 kilometers) southeast of Wilmington, its forward movement slowed to 10 mph (17 kph).
Gradually, Friday through the weekend (local time), the massive storm - containing a zone of tropical-storm-force winds almost 643km wide - will drift inland, engulfing much of SC and southern North Carolina.More news: 6 dead in Bakersfield, Calif., mass shooting
More news: Apple expected to unveil bigger, pricier iPhone on Wednesday
More news: Three Times First Lady of Pakistan: Kulsoom Nawaz
By the time the storm leaves the region, forecasters expect it to drop 50 to 75 centimeters (19-30 inches) of rain in coastal areas, with some parts capable of receiving up to 100 centimeters (40 inches).
"This rainfall would produce catastrophic flash flooding and significant river flooding", the NHC said. Operations at airports along the Carolina coastline have also been suspended.
"Your time is running out", he said.
In Charleston, the city government said that after giving out 53,000 sandbags, "there is no longer any sand available at any city of Charleston location".
"This is not going to be a glancing blow", Byard said, warning of power outages, road closures, infrastructure damage and potential loss of life.
- Hurricane Florence continues to gain strength while steadily making its way toward the East Coast.
SC ordered the mandatory evacuation of one million coastal residents while North Carolina ordered an evacuation of the Outer Banks, barrier islands that are a popular tourist destination.
"Residents in the path of these devastating storms should comply with all evacuation orders and other emergency instructions".
Georgia Governor Nathan Deal, concerned the storm would bring its devastation south, issued an emergency declaration for all 159 counties in his state.
As the southeastern coast braces for the impact of Hurricane Florence, a powerful Category 2 storm, those who live further inland could experience treacherous weather conditions as well. "The infrastructure is going to break, the power is going to go out".