Adelaide anaesthetist Richard Harris, who has 30 years of diving experience and has led cave rescue and recovery missions before, risked his own life on Saturday to make the treacherous journey to the chamber where the boys have been trapped for 15 days.

It was on his advice that the first four boys were cleared to make the incredibly dangerous journey out of the flooded cave complex, emerging alive on Sunday.

Foreign Affairs Minister Julie Bishop says the doctor’s expertise is in high demand as the rescue mission rolls on, with the aid of 19 Australians.

“He has a diving support partner with him as well. The Australian doctor was in the cave – he was part of the medical assessment to determine that the boys were fit enough to dive and swim to freedom,” she said on Monday.

Harris continues to play a key role in the ongoing international effort to get the remaining eight boys and their coach to safety.

Dr Richard Harris. Photo: AAP via Oztek

Rescue divers and the boys must dive, swim and climb their way to safety along a pitch-black tunnel that at points is barely big enough to allow an adult human body to wriggle through.

Those who know Harris say his unique set of skills to give the ongoing rescue the best chance of success.

David Strike has known Harris for more than 10 years, and says his medical expertise and experience as a cave diver and retrieval expert is invaluable.

“Richard is just one member of a team of uniquely qualified and extraordinary people prepared to sacrifice their own comfort, safety and well-being for the benefit of others. It’s an over-used term, but all of those involved are true heroes,” he told Fairfax media.

Harris has spent the past six years working for MedSTAR, an aeromedical retrieval service for the South Australian ambulance service.

His exploration and photography have gained him a following in the international cave diving community.

He is a leading expert in cave rescue expertise in Australia, and in 2011, had the difficult task of recovering the body of his friend, cave diver Agnes Milowka, after she ran out of air in Tank Cave at Millicent, near Mount Gambier.

After that operation, he spoke of seeing his friend’s body submerged in about 20 metres of water, half a kilometre from the mouth of the cave. She had run out of air after becoming separated from her dive buddy and could not find her way out.

“It looks like she has remained very calm right to the very last breath while she has been working to extricate herself,” Harris told The Australian at the time.

Meanwhile, eight young soccer players and their coach are continuing to wait for a team of top cave divers to lead them on the treacherous journey out of the flooded cave.

Four boys were safely guided through four kilometres of cold, murky water and narrow, rocky tunnels to finally exit the Tham Luang Nang Non cave in northern Thailand’s Chiang Rai province shortly after 8pm (local time) Sunday night.

Two cave divers accompanied each boy and were met with cheers of joy and applause when they finally made it to the cave’s mouth in a rescue mission that has captured the world’s attention.

The four boys are now being treated in a provincial hospital but there is no news yet on their conditions.

Chiang Rai’s acting Governor Narongsak Osatanakorn said after the first group of boys were successfully rescued, the divers would take a 10 to 20-hour pause in operations so scuba tanks could be replenished with oxygen.

The boys, many of whom are not confident swimmers, have been given training in scuba diving so they can navigate the flooded passageways, with one measuring just 38cm in diameter.

“The operation went much better than expected,” Osatanakorn, the leader of the rescue mission, said on Sunday night.

But with more rain predicted the pressure is on to remove all the group.

The news comes as Elon Musk’s Space X rocket company continues to test a “tiny kid-sized submarine” that it believes will be able to help free the children.

The mini-sub was being tested in California and, if successful, it will be flown on a 17-hour flight to Thailand, a spokesman for Musk’s Boring Co. said, adding that Thai officials had requested the device.

A video of the testing has been posted on Twitter.

Six Australian Federal Police divers are supporting the Thai Navy in the mission, together with a liaison officer and interpreter.

The divers formed part of the ‘daisy chain’ of rescuers who led the four boys to the surface on Sunday.

Cave rescue experts consider an underwater escape to be a last resort, especially with people untrained in diving.

The death Friday of a former Thai navy SEAL, Saman Gunan, underscored the risks. The diver, the first fatality of the rescue effort, was working in a volunteer capacity and died on a mission to place oxygen canisters along the route.

– AAP with AP