Bangkok: Tech entrepreneur Elon Musk has gone on a bizarre Twitter rant in defence of his offer to help the Thai cave rescue operation, calling one of the British divers a "pedo".

Vern Unsworth, a British diver who helped rescue the 12 boys and their soccer coach trapped in the Tham Luang cave, dismissed Musk's offer to build a miniature submarine as a publicity "stunt".

"He can stick his submarine where it hurts," Vern Unsworth told CNN on Saturday.

Elon Musk's child-sized submarine was deemed "impractical" for the Thai cave rescue mission. Credit:Fairfax Media

"It just had absolutely no chance of working. He had no conception of what the cave passage was like. The submarine was about five foot six [1.7 metres] long, rigid, so it wouldn't have gone 'round corners or 'round any obstacles. It wouldn't have made the first fifty metres into the cave... just a PR stunt."