Charles Gregory, 25, went missing 12 miles offshore after he set out in a 12ft jon boat on Friday, the US Coast Guard said.

His family reported him missing later that day after he did not return to St Augustine.

Mr Gregory had set out for an early morning fishing trip when a wave hit his flat-bottomed vessel, knocking him into the water, CNN reported.

He managed to get back on board but was swept out to sea and "struggled to stay alive" under the Florida sun, his father told the network.

"He was scared to death," Raymond Gregory said, describing how his son suffered jellyfish stings and saw sharks during his ordeal.

"He said he's had more conversations with God in that 30 hours than he's had his whole life."

A Coast Guard plane eventually spotted Mr Gregory sitting in the partially submerged boat on Saturday morning.

Footage of the rescue shows a boat crew approaching the stricken vessel as Mr Gregory waves, his feet beneath the water.

The Coast Guard crew then transferred him to shore and then to the emergency medical services, who took him to hospital.

No medical concerns were reported, the Coast Guard said.

'Don't ever give up'

Mr Gregory's father said his son had suffered sunburn during the day and struggled to stay warm at night.

"At night being sunburnt, and the wind would be blowing, he said it was freezing cold out there in that water," he said.

"At the end of the day, the whole moral of the story is 'don't ever give up'."

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Coast Guard Sector Jacksonville Commander Nick Barrow said he was "pleased with the outcome" of rescuing Mr Gregory from a "life-threatening situation".

"It highlights the importance of having safety gear onboard and being prepared for the worst," he said.

"If you plan to head out on the water, remember to have a life jacket, VHF marine grade radio, signalling devices and an emergency personal locator beacon to contact first responders in case you are in need of assistance."