North Carolina officials on Monday ordered residents to evacuate the state's Outer Banks barrier islands beginning on Monday ahead of Hurricane Florence, the first major hurricane to threaten the eastern United States this year.
With winds of 115 miles per hour (185 kph), the storm had reached Category 3 strength on the five-step Saffir-Simpson scale by 11 am on (1500 GMT) on Monday, according to the National Weather Service.
It warned the storm would be "an extremely dangerous major hurricane" by the time it made landfall, forecast in the Carolinas on Thursday.
The hurricane was gaining strength as it travelled over warm Atlantic waters, about 1,240 miles (2,000 km) east-southwest of Cape Fear, North Carolina, the National Hurricane Center said in an advisory.
All of Hatteras Island was under mandatory evacuation order and other parts of the Outer Banks will have to evacuate by 7am EDT (1100 GMT) on Tuesday, Dare County Emergency Management said in a statement.
Hurricane-force winds could buffet the Carolinas by Wednesday night with landfall likely in South Carolina and North Carolina on Thursday, followed by heavy rains that could cause flooding in much of the US Southeast, the NHC said.
The governors of Virginia, North Carolina and South Carolina all declared states of emergency.
Residents as far north as Virginia were warned that Florence could bring a life-threatening coastal storm surge, as well as inland flooding from "prolonged and exceptionally heavy rainfall," the NHC said.