Hurricane Florence is expected to strengthen into a near-Category 5 storm as it approaches the US where 1.7 million people have been warned to get out of the way.
The storm taking aim at the Carolinas is likely to bring “life-threatening, catastrophic flash flooding and significant river flooding” when it sweeps in on Thursday and Friday, the National Weather Service (NWS) said.
President Donald Trump has declared states of emergency for North and South Carolina and Virginia, saying the US government is “absolutely, totally prepared” for Florence.
At 8am local time on Wednesday, the “monster” storm was centred 530 miles south east of Cape Fear, approaching the coast of North Carolina at 17mph.
The National Hurricane Centre said 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 157mph or higher.
The coastal surge from Florence could leave the eastern tip of North Carolina under more than 9ft of water in spots, projections showed.
The hurricane is forecast to dump 1ft to 2ft 6in of rain that could cause flooding well inland and wreak environmental havoc by washing over industrial waste sites and farms.
Motorists were streaming inland on highways converted to one-way evacuation routes after forecasters and politicians pleaded with the public to take the warnings seriously.
“This storm is a monster. It’s big and it’s vicious. It is an extremely dangerous, life-threatening, historic hurricane,” North Carolina governor 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.”
More than 5.4 million people live in areas under hurricane warnings or watches on the US East Coast, according to the NWS, and another four million were under a tropical storm watch.
North and South Carolina and Virginia 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 ahead of its eye, and so wet that a swathe 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, North Carolina, and inland Raleigh.
Between the two cities, about two hours apart, the traffic flowed smoothly in places and became gridlocked in others because of minor collisions.
Only a trickle of vehicles was going in the opposite direction, including pick-up trucks carrying plywood and other building materials.
Long lines formed at service stations and some started running out of fuel.
“This one really scares me,” National Hurricane Centre director Ken Graham said.
Federal officials urged 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 20in of rain, if not more, with as much as 10in elsewhere in the state and in Virginia, parts of Maryland and Washington DC.
One trusted computer model, the European simulation, predicted more than 45in in parts of North Carolina.
The European model was accurate in predicting 60in for Hurricane Harvey in the Houston area in 2017.
Florence has forced people to cut their holidays short along the coast, while the storm’s projected path includes half a dozen nuclear power plants, pits holding coal-ash and other industrial waste, and numerous pig 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.