US emergency officials have warned “time is running out” for people to escape from Hurricane Florence as outer bands of wind and rain began lashing North Carolina.

Florence’s winds have dropped from a peak of 140mph to 105mph, reducing the hurricane from a Category 4 to a Category 2.

But forecasters warned that the widening storm — and the likelihood of it lingering around the coast for days — would bring seawater surging on to land and torrential downpours.

“It truly is really about the whole size of this storm,” National Hurricane Centre director Ken Graham said. “The larger and the slower the storm is, the greater the threat and the impact — and we have that.”

Federal Emergency Management Agency administrator Brock Long said storm surge warnings have not changed despite the weakening intensity of the winds.

He urged people in the coastal Carolinas and living near inland rivers to evacuate. “Please heed the warnings,” Mr Brock said: “Your time is running out.”

Hurricane FlorenceHurricane Florence churns over the Atlantic as seen from the International Space Station (Alexander Gerst/ESA/NASA via AP)

As of 11am local time, Florence was centred about 145 miles south east of Wilmington and its forward movement slowed to 10mph. Hurricane-force winds extended 80 miles from its centre, and tropical storm force winds up to 195 miles.

Forecasters said Florence’s eye could come ashore early on Friday around the North Carolina-South Carolina border. Then it is likely to hover along the coast on Saturday, pushing up to 13ft of storm surge.

The forecast suggests as much as 40in of rain over seven days along the coast, with the deluge continuing even as the centre of the storm pushes its way over the Appalachian Mountains.

The result could be what the Houston area saw during Hurricane Harvey just over a year ago – catastrophic inland flooding that could swamp homes, businesses, fields and industrial sites.

The result could be catastrophic inland flooding that could swamp homes, businesses, fields and industrial sites.

The police chief of a barrier island in Florence’s approach said he was asking for next-of-kin contact information from the few residents who refused to leave.

“I’m not going to put our personnel in harm’s way, especially for people that we’ve already told to evacuate,” Wrightsville Beach police chief Dan House said.

US hurricane(PA Graphics)

North Carolina governor Roy Cooper urged residents to remain alert despite changing forecasts.

“Don’t relax, don’t get complacent. Stay on guard. This is a powerful storm that can kill. Today the threat becomes a reality,” he said.

About 5.25 million people live in areas under hurricane warnings or watches, and 4.9 million 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 100mph, but that is still enough to cause at least $1 billion in damage. Water kills more people in hurricanes than wind does.

It is unclear exactly how many people fled, but more than 1.7 million people in the Carolinas and Virginia were warned to clear out.

Tropical Weather South CarolinaPeople have been urged to leave their homes as the hurricane approaches (Mic Smith/AP)

Airlines cancelled nearly 1,000 flights and counting. Home Depot and Lowe’s activated emergency response centres to get generators, rubbish 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 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.

Florence’s weakening as it neared the coast created tension between some who left home and authorities who worried that the storm could still be deadly.

Frustrated after evacuating his beach home for a storm that has since been downgraded, retired nurse Frederick Fisher grumbled in the lobby of a hotel in Wilmington several miles inland.

“Against my better judgment, due to emotionalism, I evacuated,” he said. “I’ve got four cats inside the house. If I can’t get back in a week, after a while they might turn on each other or trash the place.”