The National Weather Center said Florence will likely be "the storm of a lifetime" for portions of the Carolina coast.
The National Hurricane Center said the storm will eventually push westward and make a right hook to the northeast over the southern Appalachians, moving into the mid-Atlantic region and New England as a tropical depression by the middle of next week.
Up to 1.7 million people in North Carolina, South Carolina and Virginia have been given voluntary or mandatory evacuation orders, according to emergency management officials, as the storm churned across the Atlantic Ocean towards the coast. Governors of those states have already declared states of emergency, as have the governors of Virginia and Maryland.
Trump declared states of emergency for North and SC and Virginia, opening the way for federal aid.
"The sun rose this morning on an extremely risky situation and it's going to get worse", he said at a news conference in Raleigh. Forecasters said Florence could become an extremely risky major hurricane sometime Monday and remain that way for days. Regardless of the exact path, impacts will extend well beyond the center and into southeast SC.
More than 400 hundred officers from the South Carolina Law Enforcement Division will be stationed in the coastal areas to help assists evacuation and protect property.
Now a Category 3 storm, Florence is sustaining winds at 135 miles per hour.
Hurricane-force winds will bring down trees and damage homes and businesses. Florence is now heading for ocean water with surface temperatures of around 85 degrees, meaning it will likely strengthen on its way to the East Coast.More news: U.S. capital under state of emergency for Hurricane Florence
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People in areas vulnerable to a risky hurricane have left or are fleeing ahead of the storm's expected Friday or Saturday landfall.
Satellite images show the storm has maintained a distinct eye and is well organized.
Maximum sustained winds are approaching 130mph, with higher gusts expected.
"This is a life-threatening situation", the center said in an early morning bulletin. Landfall could take place Friday or Saturday morning at this point.
Enough rain could fall to break North Carolina's record for a tropical storm - 24 inches - set near Wilmington during Hurricane Floyd in 1999, said Greg Carbin, chief of forecast operations at the Weather Service's national prediction center.
The slow movement, combined with the massive amount of moisture this storm holds, will bring risky rains - from 20 to 30 inches in coastal North Carolina, with 40 inches possible in isolated areas, the weather service says.
Early on Friday, the downtown area of the city of New Bern, on the Trent and Neuse rivers near the North Carolina coast, was underwater as emergency crews conducted several rescues, according to reports on social media.