Florence's top sustained wind speeds dropped from a high of 140 mph (225 kph) to 110 mph (175 kph) as its outer rain bands approached the North Carolina coast early Thursday, reducing the storm from Category 4 to Category 2, but forecasters warned that the enormous wind field has been growing larger, raising the risk of the ocean surging on to land.
PHOTOS: Traffic jams and boarded windows as Southeast braces for storm
"Do you want to get hit with a train or do you want to get hit with a cement truck?" said Jeff Byard, an administrator with the Federal Emergency Management Agency.
As of 5 a.m. EDT it was centered about 205 miles (325 kilometers) east-southeast of Wilmington, North Carolina and about 250 miles (450 kilometers) east-southeast of Myrtle Beach, South Carolina, moving northwest at 15 mph (24 kph).
RELATED: What is a hurricane?
The National Hurricane Center's best guess was that Florence's eye would blow ashore as early as Friday afternoon around the North Carolina-South Carolina line. Then, it will likely hover along the coast Saturday, pushing up to 13 feet (nearly 4 meters) of storm surge and dumping 20 to 30 inches (50 to 75 centimeters) of rain on both states, before slogging over the Appalachian Mountains.
The result: catastrophic inland flooding that could swamp homes, businesses, farm fields and industrial sites.
About 5.25 million people live in areas under hurricane warnings or watches, and 4.9 million more live in places covered by tropical storm warnings or watches, the National Weather Service said.
Weather Underground meteorology director Jeff Masters said Florence eventually could strike as a Category 1 with winds less than 100 mph (160 kph), but that's still enough to cause at least $1 billion in damage. Water kills more people in hurricanes than wind, and the rain and storm surge will make Florence extremely dangerous.
President Donald Trump both touted the government's readiness and urged people to get out of the way. "Don't play games with it. It's a big one," he said at the White House.
WATCH: Highway traffic reversed as people flee Hurricane Florence
It's unclear exactly how many people fled, but more than 1.7 million people in the Carolinas and Virginia were warned to clear out. Airlines canceled nearly 1,000 flights and counting. Home Depot and Lowe's activated emergency response centers to get generators, trash bags and bottled water to stores before and after the storm. The two hardware chains said they sent in a total of around 1,100 trucks.
Duke Energy, the nation's No. 2 power company, said Florence could knock out electricity to three-quarters of its 4 million customers in the Carolinas, and outages could last for weeks. Workers are being brought in from the Midwest and Florida to help in the storm's aftermath, it said.
Boarding up his home in Myrtle Beach, South Carolina, Chris Pennington watched the forecasts and tried to decide when to leave.
"In 12 or 18 hours, they may be saying different things all over again," he said.
Computer models of exactly what the storm might do varied, adding to the uncertainty. Reacting to the possibility of a more southerly track, Georgia Gov. Nathan Deal declared an emergency but did not immediately order any evacuations.
"I ask all Georgians to join me in praying for the safety of our people and all those in the path of Hurricane Florence," Deal said.
In Virginia, where about 245,000 residents were ordered to evacuate low-lying areas, officials urged them to stay in safer locations despite forecast changes showing Florence's path largely missing the state.
With their entire neighborhood evacuated in Wilmington, North Carolina, David and Janelle Garrigus planned to ride out Florence at their daughter's one-bedroom apartment in Charlotte. Unsure of what they might find when they return home, the couple went shopping for a recreational vehicle.
"We're just trying to plan for the future here, not having a house for an extended period of time," David Garrigus said.
Melody Rawson evacuated her first-floor apartment in Myrtle Beach and arrived at Atlanta Motor Speedway in Hampton, Georgia, to camp for free with three other adults, her disabled son, two dogs and a pet bird.
"We hope to have something left when we get home," she said. Three other Southern raceways also opened campgrounds to evacuees.
Forecasters worried the storm's damage will be all the worse if it lingers on the coast. The trend is "exceptionally bad news," said University of Miami hurricane researcher Brian McNoldy, since it "smears a landfall out over hundreds of miles of coastline, most notably the storm surge."
With South Carolina's beach towns now more in the bull's-eye because of the shifting forecast, Ohio vacationers Chris and Nicole Roland put off their departure from North Myrtle Beach to get the maximum amount of time on the sand. Most other beachgoers were long gone.
"It's been really nice," Nicole Roland said. "Also, a little creepy. You feel like you should have already left."
RELATED FROM ABC NEWS: What to expect and when from Hurricane Florence
AccuWeather warns this hurricane could cause catastrophic inland flooding in the Carolinas and Virginias.
See more stories, photos, and video on Hurricane Florence.