One of the rescuers who helped save the 12 trapped Thai soccer players and their coach from a treacherous flooded cave has slammed Elon Musk's offer of help as nothing but a PR stunt.

The Tesla and SpaceX founder brought a mini submarine to Thailand which he suggested could be used to get the boys out, but the idea was rejected by officials as "not practical".

British diver Vern Unsworth, 63, a key member of the rescue team, shot down Mr Musk's idea in an interview about the ordeal with CNN.

"He can stick his submarine where it hurts," Mr Unsworth said.

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"It had absolutely no chance of working. He had no conception of what the cave passage was like.

"The submarine, I believe, was about five foot six long, rigid, so it wouldn't have gone round corners or round any obstacles," he explained.

"It wouldn't have made the first 50 metres into the cave from the dive start point. Just a PR stunt."

Mr Unsworth, who lives in Thailand and regularly explores the Tham Luang caverns in Chiang Rai where the boys and their coach became trapped, said he was not impressed when the tech billionaire showed up at the site, adding he was "asked to leave very quickly".

"And so he should have been."

Elon Musk's mini submarine has been widely slammed by those involved in the rescue efforts. Picture: Supplied
Elon Musk's mini submarine has been widely slammed by those involved in the rescue efforts. Picture: Supplied

The boys are in hospital recovering from their 17 days underground. A hospital spokesman confirmed on Saturday that they will be released on Thursday.

In videos the boys filmed from their hospital beds, they expressed their gratitude and revealed what they are most looking forward to eating as soon as they are well enough.