Governor Roy Cooper called the storm, which was downgraded from a hurricane after it made landfall, an “uninvited brute”.
“The fact is this storm is deadly and we know we are days away from an ending,” Cooper said.
At least five people, including a mother and her child, have been killed as Florence brings unending rain and storm surges to the region.
Some towns have experienced as much 60 centimetres of rain, and forecasters warn that could rise to a metre of downpours, triggering floods deep inland.
Storm surges – the bulge of ocean water pushed ashore by the hurricane – were as high as three metres.
The 640km-wide storm has struck regions as far north as New York state and left hundreds besieged by waters.
Rescue crews used boats to reach more than 360 people stranded by rising waters in New Bern, North Carolina, while many of their neighbours awaited help.
Officials said some 1.7 million people in the Carolinas and Virginia were warned to evacuate, but it’s unclear how many did. The homes of about 10 million were under watches or warnings for the hurricane or tropical storm conditions.
Coastal towns in the Carolinas were largely empty, and schools and businesses closed as far south as Georgia.
The storm knocked out power to nearly 930,000 homes and businesses, and the number could keep rising.
Florence could become a major test for the Federal Emergency Management Agency, which was heavily criticised as slow and unprepared last year for Hurricane Maria in Puerto Rico, where the death toll was put at nearly 3,000.
Forecasters said that given the storm’s size and sluggish track, it could cause epic damage akin to what the Houston area saw during Hurricane Harvey just over a year ago, with floodwaters swamping homes and businesses and washing over industrial waste sites and hog-manure ponds.