National Hurricane Center says swells generated by Florence are affecting Bermuda and portions of the U.S. East Coast. Since reliable record-keeping began more than 150 years ago, North Carolina has only been hit by one Category 4 hurricane - Hazel, with 130mph winds, in 1954.
The category 4 hurricane is expected to hit as an "extremely unsafe hurricane" NHC says, despite predictions of some weakening after the next 48 hours.
The large and powerful hurricane has prompted evacuation orders in North and SC and Virginia, as officials urge residents in coastal and low-lying areas to prepare for strong winds, a deep storm surge and a deluge of rainfall that could last more than 24 hours.
President Donald Trump declared that an emergency exists in North Carolina, ordering federal assistance for the state as it braces for the powerful storm, and will look to recover from possible damage caused by Florence.
Gov. Roy Cooper of North Carolina warned residents to take the threat of the storm seriously.
North Carolina seems to be the state that could bear the brunt of the winds, along with SC and parts of southern Virginia.
The alerts also mean risky storm surges are likely along the coast and heavy, sustained rains could cause life-threatening flooding inland, the National Hurricane Center warned.
Trump said the hurricane was "one of the worst storms to hit the East Coast in many years".
South Carolina's governor ordered the state's entire coastline to be evacuated starting at noon Tuesday and predicted that 1 million people would flee.More news: Homeless Samaritan will get cash; couple under investigation
Officials in North Carolina have already issued mandatory evacuation orders for coastal Dare County and Hatteras Island.
It's feared Hurricane Florence could also cause a lot of flooding, with more than 50cm of rain expected in some areas.
Evacuation shelters will open on Tuesday and be available to individuals based on need, said Kim Stenson, director of the South Carolina Emergency Management Division.
This storm is lined up behind Florence in the Atlantic.
Trump said in a Twitter message he had spoken to the governors of North and SC and Virginia, adding: "Federal government stands by, ready to assist".
In Holden Beach, North Carolina, in the storm's path, longtime residents were boarding up homes and securing possessions.
Two other storms were spinning in the Atlantic as the 2018 hurricane season reaches its peak.
According to the NHC, the region is facing "life-threatening" storm surge, freshwater flooding and damaging hurricane-force winds.
She said her house, built in 2009 in Buxton, North Carolina, is on a ridge and built to withstand a hurricane. According to CNN, odds are good that it will have strengthened to Category 4 status-meaning sustained winds in the range of 130-156 miles per hour-before the time it makes landfall later this week, likely on Thursday or Friday.