At least 40 people have been killed across four states after Hurricane Helene barrelled its way across southeastern US.

Emergency crews are racing to rescue people trapped in flooded homes after Helene struck the coast of Florida as a highly destructive Category 4 storm.

It generated a massive storm surge, wreaking a trail of destruction extending hundreds of miles north.

Millions are without power in Florida and neighbouring states.

Meanwhile, dozens of people are trapped on the roof of a flooded Tennessee hospital, with a “dangerous rescue operation” under way.

The Unicoi County Hospital is engulfed in “extremely dangerous and rapidly moving water”, according to Tennessee’s Ballad Health.

It said 54 people were relocated to the roof of the Unicoi County Hospital, while seven were in rescue boats.

“The situation at the hospital is very dangerous and TEMA [The Tennessee Emergency Management Agency] and National Guard resources are engaged in what can only be described as a dangerous rescue operation,” Ballad Health added.

Local official Michael Baker told Sky News people are being moved from the roof “little by little”, describing the flooding as “unprecedented”.

“We’ve never seen anything like this,” he said.

As of early afternoon, Helene, which has been downgraded to a tropical depression, was packing maximum sustained winds of 35 mph (55 kph) as it slowed over Tennessee and Kentucky, the National Hurricane Center said.

It struck overnight with maximum sustained winds of 140 mph (225 kph) in the rural Big Bend area, the northwestern part of Florida.

The National Hurricane Center said preliminary information shows water levels reached more than 15ft above ground in that region.

US President Joe Biden has approved emergency declaration requests from the governors of several southern states affected by Helene.

Georgia, Florida, Alabama, North Carolina and South Carolina are being supported by emergency response personnel including search and rescue teams, medical support staff and engineering experts.

Georgia Governor Brian Kemp has said dozens of people are trapped in buildings damaged by the storm, with multiple hospitals in southern Georgia without power.

In western North Carolina, Rutherford County emergency officials have told residents near the Lake Lure Dam to immediately evacuate to higher ground, warning “Dam failure imminent”.

Meanwhile, Florida Governor Ron DeSantis said the damage from Helene in the area appears to be greater than the combined damage of Idalia and Hurricane Debby in August. “It’s demoralizing,” he said.

Many stranded in places like Tampa could only be reached by boat, with officials warning the water could contain live wires, sewage, sharp objects and other debris.

More than four million properties are without power across Florida, Georgia, the Carolinas, Virginia, Kentucky, Tennessee and Ohio, according to the logging website, PowerOutage.

Why this hurricane season is defying forecasts

Tom Clarke

Science and technology editor

@t0mclark3

Despite Helene’s power, this hurricane season has been more remarkable for its lack of activity.

At the start of the hurricane season, which runs from 1 June to 30 November, sea surface temperatures were (and remain) off-the-charts warm.

It’s this ocean heat that fuels tropical storms.

This combined with a developing La Nina phenomenon led the US forecasters to predict 2024 would be a major hurricane season. Between 17 and 24 storms were expected, with eight to 13 developing into hurricanes.

Hurricane Beryl grazed the coast of Jamaica in July as a Category 5 hurricane. It was the earliest storm of that size ever recorded and was seen as a harbinger of the prediction. But, so far at least, it’s failed to materialise.

There have been just six hurricanes so far this year – slightly below average. But why?

It seems to be due to what’s happening on the other side of the Atlantic where ocean warming forced the African monsoon further north than usual.

This led to catastrophic flooding in central and west Africa displacing millions, but it also shifted the weather system that usually spawns hurricanes and spins them across the Atlantic.

There’s already abundant evidence our warming oceans and atmosphere are making storms more intense – but predicting where they will occur and how often is never simple – and perhaps getting even harder as our planet gets hotter.

Prior to the hurricane making landfall, officials in Florida begged residents to evacuate. The sheriff’s office in rural Taylor County issued a chilling warning to those who refused to leave.

“Please write your name, birthday, and important information on your arm or leg in a permanent marker so that you can be identified and family notified,” the post on Facebook said.

Forecasters now expect the storm to continue weakening across Tennessee and Kentucky.

It is feared heavy rain over the Appalachian Mountains could cause mudslides and flash flooding.

Helene has made landfall in northwestern Florida as a Category 4 hurricane, with forecasters warning of a “catastrophic” storm surge.

The National Hurricane Centre in Miami said Helene struck near the mouth of the Aucilla River in the Big Bend area of Florida’s Gulf Coast at around 11.10pm local time.

High winds, possibly in excess of 140mph (225kph), and flash floods are possible, the weather service said.

Florida Governor Ron DeSantis told reporters one person had died while driving on a motorway when a sign fell on to their car.

“When Floridians wake up tomorrow morning, we’re going to be waking up to a state where, very likely, there’s been additional loss of life. And certainly, there’s going to be loss of property,” Mr DeSantis said.

“You’re going to have people that are going to lose their homes because of this storm. So please keep those folks in mind, keep them in your prayers.”

Two other people are reported to have been killed in a possible tornado in neighbouring south Georgia as the storm approached, the Associated Press reported.

‘Unsurvivable scenario’ to play out

More than one million homes and businesses were already without power shortly after the hurricane made landfall, according to tracking website poweroutage.

States of emergency have been declared in Florida, Georgia, and the Carolinas, with hurricane and flash flood warnings in place as far away as south-central Georgia.

Officials pleaded with residents in the path of the storm to heed mandatory evacuation orders or face life-threatening conditions.

The surge caused by the hurricane – the wall of seawater pushed on land by hurricane-force winds – could rise as high as 20ft (6.1m) in some spots, as tall as a two-storey house, Michael Brennan, director of the hurricane centre, said in a video briefing.

“A really unsurvivable scenario is going to play out” in the coastal area, Mr Brennan said, with water capable of destroying buildings and carrying cars pushing inland. Millions of people are under the current flood watch.

Forecasters warned the storm surge could be particularly “catastrophic and unsurvivable” in Apalachee Bay.

‘It’s going to cause a lot of damage’

Residents in the city of Tallahassee told Sky’s US partner NBC News that they stocked up on sandbags, food and supplies, before leaving their homes.

The city’s mayor John Dailey urged people to take the evacuation warnings “extremely seriously”, calling Helene “the biggest storm in the history of the city to hit us head-on”.

Speaking to NBC News on Wednesday, Mr Dailey said though they are “very prepared”, he was also “very nervous, and I hope everyone is nervous”.

He added: “This is a big storm. It is going to cause a lot of damage.”

Jared Miller, sheriff of Wakulla County, went further – calling the storm “not a survivable event for those in coastal or low-lying areas”.

The county has issued a mandatory evacuation order, but one resident, Christine Nazworth from Crawfordville, which is located about 25 miles (40km) from Apalachee Bay, said her family would be sheltering in place.

She said: “I’m prayed up. Lord have mercy on us. And everybody else that might be in its path.”

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Leslie Powell, from Quincy, a city a similar distance from Tallahassee, told NBC she was leaving her mobile home to go to a shelter with her eight-month-old baby and six-year-old daughter.

She said simply: “I’m scared. I’ve got a lot of trees around my home, so it’s not safe for me and my kids.”

Helene is expected to remain a full-fledged hurricane as it rolls through the Macon, Georgia, area on Friday, forecasters said.

Sir Keir Starmer is to meet with Donald Trump later tonight.

It is believed to be the first meeting between the current UK prime minister and former – and potentially future – US president.

The pair are set to meet overnight UK time, which is the evening in New York, where Sir Keir is currently located while on a visit to the UN.

David Lammy, the Labour foreign secretary, has met Mr Trump‘s vice presidential candidate, JD Vance.

Speaking to journalists, Sir Keir reiterated he wanted to meet both Mr Trump and Kamala Harris ahead of the November vote.

However, meeting the Democrat is hard due to the “usual diary challenges”.

Sir Keir said: “It’ll be really to establish a relationship between the two of us.

“I’m a great believer in personal relations on the international stage.

“I think it really matters that you know who your counterpart is in any given country, and know them personally, get to know them face to face.

“So it’s really along those lines. I won’t go into what we’ll actually discuss, obviously, but that’s the purpose of it, as you’d expect, ahead of the election.”

Asked if a Trump presidency would leave Ukraine exposed, Sir Keir said the nature of the “special relationship” between the UK and US “always sits above whoever holds the particular office”.

“The US people will decide who they want as their president, and we will work with whoever is president,” he added.

“I’m not going to speculate on what any particular issues may be on the other side of the election.”

Speaking ahead of the meeting, Mr Trump said he thought Sir Keir was “very nice”.

He said: “I actually think he’s very nice. He ran a great race, he did very well, it’s very early, he’s very popular.”

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Mr Trump went on to praise Reform UK leader Nigel Farage as well, saying: “I think Nigel is great, I’ve known him for a long time.”

“He had a great election too, picked up a lot of seats, more seats than he was allowed to have actually.

“They acknowledged that he won but for some reason you have a strange system over there, you might win them but you don’t get them.”

This appears to be a misunderstanding of how the UK’s first past the post system for elections chooses MPs – Reform won fewer seats compared to its vote share because it came second in many seats.