Hurricane Ian is gaining strength and now on course north to South Carolina after devastating a large cross-section of Florida.

Emergency crews were wading through water and using boats on Thursday to rescue stranded Florida residents after the storm front tore a coast-to-coast path of destruction across the state, leaving behind deadly floodwaters, downed power lines and widespread damage.

Ian, one of the strongest storms ever to hit the US mainland, flooded Gulf Coast communities and knocked out power to millions before plowing across the peninsula to the Atlantic Ocean, where it regained strength ahead of another anticipated landfall in South Carolina on Friday.

It is now forecast to produce life-threatening flooding, storm surge and strong winds across Georgia and North and South Carolina, the National Hurricane Center said.

Florida governor Ron DeSantis called the damage in his state “historic” and disaster officials believe thousands could be displaced in the long term.

US President Joe Biden has declared a major disaster, releasing federal funds to pay for measures such as temporary housing for those displaced.

Ian was a category four storm with winds up to 150mph when it struck southwest Florida on Wednesday, making it the joint fifth-strongest hurricane to hit America.

Lee County sheriff Carmine Marceno told US media, deaths could be “in the hundreds” and that he’d received thousands of 911 calls.

“It crushed us,” Sheriff Marceno said. “We still cannot access many of the people that are in need.”

But Florida’s governor said the remark was speculation based on the deluge of 911 calls – and he hoped many of those people would have stayed safe.

Mr DeSantis said there were so far two unconfirmed fatalities, possibly related to the storm.

One is believed to be a 72-year-old man killed near Daytona Beach after going outside to drain his swimming pool during the storm.

South and North Carolina are now bracing for impact, as Ian – which had weakened to a tropical storm during its trek across Florida – returned to hurricane strength by 5pm eastern American time (10pm UK).

Electricity remained cut for 2.6 million in Florida on Thursday evening, according to website Power Outage US.

There was virtually no mobile phone service in some areas, and internet connectivity was also affected.

Walt Disney World and other tourist attractions in central Florida appeared to have avoided severe damage from Ian, but many businesses on the state’s southwestern coast – also a tourist hotspot – were destroyed and face a long rebuilding process.

300 trucks of food and water heading out

In Port Charlotte, about 65 miles south of Tampa, the surge flooded a hospital emergency room and ripped off part of the intensive care unit’s roof.

“We’ve never seen a flood event like this,” said Florida’s governor at a media conference on Thursday morning.

“We’ve never seen storm surge of this magnitude – and it hit an area where there’s a lot of people… It’s going to end up doing extensive damage to a lot of people’s homes.”

Mr DeSantis said bridges were being inspected for safety, but the causeway to Sanibel island was impassable after a chunk fell into the sea and cut off more than 6,000 people.

More than 300 trucks containing food and water are also being sent to southwest Florida, said officials, who warned the storm remained a major threat to the state.

Thousands of people could be displaced in the long term due to the “catastrophic” damage, Deanne Criswell, head of the Federal Emergency Management Agency, told CNN.

On its way to the US, Ian also hit Cuba and cut off power to nearly all the island’s 11 million people.