At least 45 people have died and millions have been left without power as Hurricane Helene roared through the south-eastern US.

Officials continued daring rescues with boats, helicopters and large vehicles to help those stranded in floodwaters - including about 50 workers and patients who crowded on the roof of a flooded Tennessee hospital.

It was the most powerful storm on record to hit Florida's Big Bend and moved north into Georgia and the Carolinas after making landfall overnight on Thursday.

Insurers and financial institutions say damage caused by the storm could run into the billions of dollars.

Roads and houses were submerged on Friday, with one family describing to BBC News how they had to swim out of their home to safety.

Although Helene has weakened significantly, forecasters warn that high winds, flooding and the threat of tornadoes could continue.

Helene, which had been a category four storm, came ashore on Thursday night and remained a hurricane for six hours after it made landfall, according to the Federal Emergency Management Agency (FEMA).

The National Hurricane Center (NHC) said a storm surge - heightened water levels mostly caused by high winds blowing water towards shore - reached more than 15ft (4.5m) above ground level across parts of the Florida coast.

The NHC said the surge should subside before the weekend but the threat from high winds and flooding would persist, including possible landslides.

Up to 20in (50cm) of rain is still possible in places.

The hurricane is the 14th most powerful to hit the US since records began. At approximately 420 miles (675 km) wide, it is behind only two other hurricanes - Ida in 2017 and Opal in 1996, both of which were 460 miles wide.

Because of its sheer size, the impact of strong winds and heavy rain have been widespread across Florida, Georgia, Tennessee and the Carolinas.

At least eight people have died in Florida since Friday, including at least five people in the coastal Pinellas County - which includes the city of St Petersburg - the county's sheriff, Bob Gualtieri said.

He added that the nearby coastline had "never, ever looked like this before", describing it as like a "war zone".

Florida Governor Ron DeSantis said one person died after a road sign fell on their car and another when a tree fell on a home.

After hitting Florida, the storm continued on a deadly path north into Georgia - leaving at least 15 dead - including a first responder, Governor Brian Kemp said.

A suspected tornado that spawned in Wheeler County, central Georgia, left two people dead when it picked up and overturned a mobile home, authorities said.

Kemp ordered 1,000 National Guard troops to help with rescue efforts across the state. The Georgia governor said on Friday that people were still trapped in buildings.

In South Carolina, at least 17 people were killed, according to CBS News, the BBC's US partner.

Neighbouring North Carolina saw at least two fatalities in the storm, one due to a vehicle collision and another when a tree fell on a home in Charlotte, Governor Roy Cooper said.

The state also saw two confirmed tornadoes, which damaged 11 buildings and injured 15 people, the National Weather Service said.

One person was also killed in Virginia, the state's governor, Glenn Youngkin, said at a news conference on Friday.

Across the south-east, more than three million homes and businesses were without power as of Saturday morning, according to tracking site poweroutage.us.

Ahead of the storm, 1,500 federal emergency personnel were deployed to the region, including 940 search and rescue specialists.

At the same time, around 8,000 members of the US Coast Guard were assisting with rescue operations.

In North Carolina alone, more than 100 rescues have taken place, Cooper said.

In Tennessee, 58 patients and staff were left stranded on the roof of a hospital in the city of Erwin on Friday. Swift-moving water from the Nolichucky river prevented boats from being able to conduct rescue operations, and high winds prevented helicopter rescue.

The group was later taken to safety after helicopters from the Tennessee National Guard and the Virginia State Police intervened.

In Pasco County, north of Tampa on Florida's Gulf coast, 65 people were rescued. Guests at a Ramada Inn in Manatee County were also rescued as floodwaters rushed into the hotel.

In Suwannee County to the north, authorities reported "extreme destruction", with trees falling onto homes.

Along the Gulf Coast of Florida, Briana Gagnier told the BBC that she and her family saw water creeping into their home on Holmes Beach and started moving their belongings onto tables and beds before hearing a loud bang.

"My family and I all looked at one another," she said. "Then water just started pouring in."

Ms Gagnier said she grabbed her pets, her wallet and some portable chargers and swam out of their home with her family. The water was up to their shoulders.

On Friday, President Joe Biden said: "As we mourn the lives of those who were taken by this storm, I urge folks to heed the direction of local officials and take every precaution to keep themselves and their families safe."

Officials have said the effects of the storm are "not over yet", and urged residents to remain vigilant.

Hurricanes need sea surface temperatures of more than 27C (80F) to fuel them.

With exceptionally warm waters of the Gulf at 30-32C, the sea surface is about two degrees Celsius above normal for the time of year.

Florida's 220-mile Big Bend coast is where Hurricane Idalia made landfall in 2023. The area was also battered by Hurricane Debby last month.

There could be as many as 25 named storms in 2024, the National Oceanic and Atmospheric Administration (NOAA) warned earlier this year.

Between eight and 13 of those storms could develop into hurricanes and a handful already have including Helene.

More storms could be on the horizon, officials warned, as the official end of hurricane season is not until 30 November.