Florence was expected to blow ashore late Thursday or early Friday, then slow down and wring itself out for days, unloading 1 to 2½ feet (0.3 to 0.6 meters) of rain that could cause flooding well inland and wreak environmental havoc by washing over industrial waste sites and hog farms.
Forecasters and politicians pleaded with the public to take the warnings seriously and minced no words in describing the threat.
"This storm is a monster. It's big and it's vicious. It is an extremely dangerous, life-threatening, historic hurricane," North Carolina Gov. Roy Cooper said.
He added: "The waves and the wind this storm may bring is nothing like you've ever seen. Even if you've ridden out storms before, this one is different. Don't bet your life on riding out a monster."
Some hoped for divine intervention.
"I'm prayed up and as ready as I can get," Steven Hendrick said as he filled up gasoline cans near Conway, South Carolina.
More than 5.4 million people live in areas under hurricane warnings or watches on the U.S. East Coast, according to the National Weather Service, and another 4 million people were under a tropical storm watch.
President Donald Trump declared states of emergency for North and South Carolina and Virginia, opening the way for federal aid. He said the federal government is "absolutely, totally prepared" for Florence.
All three states ordered mass evacuations along the coast. But getting out of harm's way could prove difficult.
Florence is so wide that a life-threatening storm surge was being pushed 300 miles (485 kilometers) ahead of its eye, and so wet that a swath from South Carolina to Ohio and Pennsylvania could get deluged.
People across the region rushed to buy bottled water and other supplies, board up their homes, pull their boats out of the water and get out of town.
A line of heavy traffic moved away from the coast on Interstate 40, the main route between the port city of Wilmington and inland Raleigh. Between the two cities, about two hours apart, the traffic flowed smoothly in places and became gridlocked in others because of fender-benders.
Only a trickle of vehicles was going in the opposite direction, including pickup trucks carrying plywood and other building materials.
Long lines formed at service stations, and some started running out of gas as far west as Raleigh, with bright yellow bags, signs or rags placed over the pumps to show they were out of order. Some store shelves were picked clean.
"There's no water. There's no juices. There's no canned goods," Kristin Harrington said as she shopped at a Walmart in Wilmington.
At 11 p.m., the storm was centered 670 miles (1,075 km) southeast of Cape Fear, North Carolina, moving at 17 mph (28 kph). It was a potentially catastrophic Category 4 storm but was expected to keep drawing energy from the warm water and intensify to near Category 5, which means winds of 157 mph (253 kph) or higher.
Florence is the most dangerous of three tropical systems in the Atlantic. Tropical Storm Isaac was east of the Lesser Antilles and expected to pass south of Puerto Rico, Hispaniola and Cuba, while Hurricane Helene was moving northward away from land. Forecasters also were tracking two other disturbances.
The coastal surge from Florence could leave the eastern tip of North Carolina under more than 9 feet (2.75 meters) of water in spots, projections showed.
"This one really scares me," National Hurricane Center Director Ken Graham said.
Federal officials begged residents to put together emergency kits and have a plan on where to go.
"This storm is going to knock out power days into weeks. It's going to destroy infrastructure. It's going to destroy homes," said Jeff Byard, an official at the Federal Emergency Management Agency.
Forecasters said parts of North Carolina could get 20 inches (50 centimeters) of rain, if not more, with as much as 10 inches (25 centimeters) elsewhere in the state and in Virginia, parts of Maryland and Washington, D.C.
One trusted computer model, the European simulation, predicted more than 45 inches (115 centimeters) in parts of North Carolina. A year ago, people would have laughed off such a forecast, but the European model was accurate in predicting 60 inches (150 centimeters) for Hurricane Harvey in the Houston area, so "you start to wonder what these models know that we don't," University of Miami hurricane expert Brian McNoldy said.
Rain measured in feet is "looking likely," he said.
The storm forced people to cut their vacations short along the coast.
Paula Matheson of Springfield, Oregon, got the full Southern experience during her 10-week RV vacation: hot weather, good food, beautiful beaches and, finally, a hurricane evacuation.
Florence interrupted her stay on North Carolina's Outer Banks. It took Matheson and her husband nearly the whole day Monday to drive the 60 miles (100 kilometers) off the barrier island .
"It was so beautiful. The water was fabulous. Eighty-five degrees," Matheson said, pausing a moment. "I guess that's a big part of the problem."
Florence's projected path includes half a dozen nuclear power plants, pits holding coal-ash and other industrial waste, and numerous hog farms that store animal waste in huge lagoons.
Duke Energy spokesman Ryan Mosier said operators would begin shutting down nuclear plants at least two hours before hurricane-force winds arrive.
North Carolina's governor issued what he called a first-of-its-kind mandatory evacuation order for North Carolina's fragile barrier islands from one end of the coast to the other. Typically, local governments in North Carolina make the call on evacuations.
"We've seen nor'easters and we've seen hurricanes before," Cooper said, "but this one is different."
Associated Press writers Seth Borenstein in Washington; Jennifer Kay in Miami; Gary Robertson in Raleigh, North Carolina; Jeffrey Collins in Latta, South Carolina; Meg Kinnard in Columbia, South Carolina; Jeff Martin and Jay Reeves in Atlanta; and Tamara Lush in St. Petersburg, Florida, contributed to this report.
For the latest on Hurricane Florence, visit https://www.apnews.com/tag/Hurricanes .
Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.