Billionaire Elon Musk has labelled a British diver involved in the dramatic rescue of 12 trapped Thai soccer players and their coach a "pedo".

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 Musk's idea in an interview about the ordeal with CNN.

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

"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.

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

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."

But responding to a New York Times piece about what Musk should learn from the Thai rescue, the billionaire unloaded on the British diver.

"Mr Musk's desire to help was commendable. But when the head of the rescue operation, Narongsak Osottanakorn, declared that Mr Musk's contraption was impractical for the task at hand — a task that had been completed, at that point, by some of the world's top cave divers — Mr Musk responded with irritation," the Times piece stated.

On Twitter, Musk responded to the reporter's piece.

"Never saw this British expat guy who lives in Thailand (sus) at any point when we were in the caves," Musk tweeted.

"Only people in sight were the Thai navy/army guys, who were great. Thai navy seals escorted us in — total opposite of wanting us to leave."

Musk then said that the water level in the flooded cave was "actually very low".

"Water level was actually very low & still (not flowing) — you could literally have swum to Cave 5 with no gear, which is obv how the kids got in.

"If not true, then I challenge this dude to show final rescue video. Huge credit to pump & generator team. Unsung heroes here."

From there his comments got more bizarre, as he called Unsworth a "pedo guy".

"You know what, don't bother showing the video. We will make one of the mini-sub/pod going all the way to Cave 5 no problemo. Sorry pedo guy, you really did ask for it."

Unsworth initially pinpointed where he thought the boys would be in the trapped cave. They were found 200m from that spot.

He was involved in the rescue for the whole 17 days.

The "Wild Boars" football team is recovering in hospital after 18 days spent inside the Tham Luang cave, which it entered on June 23 before getting trapped by monsoon floodwaters.

Doctors say the boys are in good health following a successful three-day operation which ended on July 10, when teams of Thai Navy SEALs and international cave diving experts hauled the last five members of the team to safety.

Last Tuesday, Musk told his Twitter followers he had just returned from the Tham Luang Nang Non cave complex.

"Mini-sub is ready if needed. It is made of rocket parts and named Wild Boar after kids' soccer team," he wrote.

But the head of the rescue mission dismissed the option in favour of sticking with the plan for experienced cave divers to help the boys swim out.

"Although his technology is good and sophisticated it's not practical for this mission," Mr Narongsak said.

Musk fired back at this claim, saying the former provincial governor was "not the subject matter expert" and sharing his correspondence with leader of the dive rescue team Richard Stanton.

"Right now, I have one of the world's best engineering teams who normally design spaceships and spacesuits working on this thing 24 hours a day," Musk's email to Stanton dated July 8 read. "If it isn't needed, that would be great to know."

Stanton replied: "It is absolutely worth continuing with the development of this system in as timely a manner as feasible. If the rain holds out it may well be used."