Hurricane Helene caused dozens of deaths and billions of dollars' worth of destruction across several US states after making landfall in Florida late on Thursday.

Among at least 44 people killed in the storm were three firefighters, a woman and her one-month-old twins, and an 89-year-old woman whose house was struck by a falling tree.

Those killed were in Florida, Georgia, North Carolina, South Carolina and Virginia.

All five who died in one Florida county were in neighbourhoods where residents were told to evacuate, said Bob Gualtieri, the sheriff in Pinellas County. 

Some who stayed ended up having to hide in their attics to escape the rising water, he said, adding the death toll could rise as crews go door-to-door in flooded areas.

He said the death toll could rise as crews go door-to-door in flooded areas.

"I would just describe it, having spent the last few hours out there, as a war zone," Sheriff Gualtieri said of Helene's aftermath.

More damage than Idalia and Debby combined, governor says

Helene blew ashore near the mouth of the Aucilla River in Florida's Big Bend region as a category four hurricane late on Thursday, local time, packing winds of up to 225 kilometres per hour.

Florida Governor Ron DeSantis said the damage from Helene appeared to be greater than the combined effects of Hurricane Idalia — which hit last year just 30 kilometres south-east of Aucilla, with nearly the same ferocity — and Hurricane Debby in August.

Florida's Big Bend is a part of the state where salt marshes stretch to the horizon, and where Florida's otherwise ubiquitous condo developments and strip malls are largely absent.

It's a place where Susan Sauls Hartway and her four-year-old Chihuahua mix Lucy could afford to live within walking distance of the beach on her salary as a housekeeper.

At least, until her house was carried away by Helene.

Ms Hartway wandered around her street near Ezell Beach on Friday afternoon, searching for where the storm may have deposited her home.

“It's gone. I don't know where it's at. I can't find it,” she said of her house.

Born and raised in rural Taylor County, Ms Hartway said there is nowhere in the world she would rather be, even after Helene. 

But she's watched as wealthier residents from out of state have bought up second homes here. 

She wonders how many of them will sell out — and what will happen to the locals who have nowhere else to go.

"There's so many people down here, they don't have any place to go now. This was all they had," she said.

The community has taken direct hits from three hurricanes since August last year.

When the water hit knee-level in Kera O'Neil's home in Hudson, Florida, she knew it was time to escape.

"There's a moment where you are thinking: 'If this water rises above the level of the stove, we are not going to have much room to breathe,'" she said, recalling how she and her sister waded through chest-deep water with one cat in a plastic carrier and another in a cardboard box.

The extent of the damage in Florida began emerging after daybreak on Friday.

In coastal Steinhatchee, a storm surge — a wall of seawater pushed ashore by winds — of 2.4 to 3 metres moved mobile homes, the National Weather Service said on X.

In Treasure Island, a barrier island community in Pinellas County, boats were grounded in front yards.

The city of Tampa posted on X that emergency personnel had completed 78 water rescues of residents and that many roads were impassable because of flooding.

The Pasco County sheriff's office rescued more than 65 people.

Georgia, Carolinas, Tennessee devastated

The destruction extended far beyond Florida.

Helene quickly moved up through Georgia, the Carolinas and Tennessee — uprooting trees, splintering homes and sending creeks and rivers over their banks and straining dams.

A mudslide in the Appalachian Mountains washed out part of an interstate highway at the North Carolina-Tennessee state line.

Another slide hit homes in North Carolina, and some occupants had to wait more than four hours to be rescued, said Buncombe County emergency services assistant director Ryan Cole.

His 911 centre received more than 3,300 calls in eight hours on Friday.

"This is something that we’re going to be dealing with for many days and weeks to come," Mr Cole said.

Smaller tornadoes also hit some areas — including Nash County, North Carolina where four people were critically injured.

A lake in North Carolina which featured in the movie Dirty Dancing overtopped a dam, and surrounding neighbourhoods were evacuated. 

People also were evacuated from Newport, Tennessee amid concerns about a dam nearby.

Atlanta received a record 282.4 millimetres of rain in 48 hours, Georgia's Office of the State Climatologist said on X. 

Some neighbourhoods were so badly flooded that only car roofs could be seen poking above the water.

Millions without power as Helene weakens

Rescue services reported hundreds of calls, though none more dramatic than in rural Unicoi County in east Tennessee — where more than 50 hospital patients and staff were plucked from its roof by helicopter, as water from a flooded river surrounded the building.

The Federal Emergency Management Agency deployed more than 1,500 workers due to the storm, helping with 400 rescues by late Friday morning.

Officials urged people who were trapped to call for rescuers and not tread floodwaters, warning they can be dangerous due to live wires, sewage, sharp objects and other debris.

While Helene weakened to a tropical storm and eventually a post-tropical cyclone, it has continued to wreak havoc with heavy rains that the National Hurricane Center said would result in "catastrophic and potentially life-threatening flash and urban flooding".

More than 4.2 million customers were without power across 10 states from Florida to Ohio on Friday night, according to tracker poweroutage.us.

Several flood and flash flood warnings remained in effect in parts of the southern and central Appalachians, while high wind warnings also covered parts of Tennessee and Ohio.

Forecasters also warned of flooding in North Carolina that could be worse than anything seen in the past century.

In Georgia, an electrical utility group warned of "catastrophic" damage to utility infrastructure, with more than 100 high voltage transmission lines damaged. 

Officials in South Carolina, where more than 40 per cent of customers were without power, said crews had to cut their way through debris just to determine what was still standing in some places.

The storm was expected to hover over the Tennessee Valley on Saturday and Sunday, the National Hurricane Center said.

Climate change has exacerbated conditions that allow storms like Helene to thrive, rapidly intensifying in warming waters and turning into powerful cyclones sometimes in a matter of hours.

AP/Reuters/AFP