The centre of the hurricane's eye came ashore at about 7:15am (local time) near Wrightsville Beach close to Wilmington, North Carolina, with sustained winds of 150kph, the National Hurricane Centre (NHC) said.
The National Hurricane Center said Florence will eventually make a right hook to the northeast over the southern Appalachians, moving into the mid-Atlantic states and New England as a tropical depression by the middle of next week.
"It's an uninvited brute who doesn't want to leave". "Catastrophic effects will be felt".
He added that around 20,000 people had taken refuge in 157 emergency shelters throughout the area.
In Craven County, authorities say they have received more than 150 telephone calls from people in the historic town of New Bern asking to be rescued because water has entered their homes.
New Bern is experiencing devastating flooding, as it sits at the confluence of two rivers, which are swollen as a result of the heavy rainfall.
"I'm anxious about what I might find when I go home, though", she said. "The water looming over Dr. Navarro is a brilliant way of showing the dangers of storm surge". We have steps on the sides of the house so it's a few feet off the ground anyway. "I couldn't even imagine", he said.More news: Final Fantasy XV: Pocket Edition HD for Switch launches today
A mother and baby were killed when a tree fell on a house, according to a tweet from Wilmington police. Hundreds more were rescued elsewhere from rising water.
Hurricane Florence has barrelled into the Carolina coast and moved inland, knocking down trees, overflowing rivers, dumping sheets of rain and leading to the death of five people before it was downgraded to a tropical storm still capable of wreaking havoc.
The center said the threat of freshwater flooding will increase over the next several days.
The Category 1 storm has maximum sustained winds of 90 miles per hour and is moving slowly, at 6 miles per hour.
The storm's movement, not its strength, has forecasters and officials anxious.
Given the storm's size and slow speed, officials warned that Florence could cause similar large-scale flood damage to that seen in the Houston area during Hurricane Harvey just over a year ago.
It is expected to move across parts of south-eastern North Carolina and eastern SC on Friday and Saturday, then head north over the western Carolinas and central Appalachian Mountains early next week, the NHC said.