Dive operator Charlie Fitzgerald, of Batemans Bay Dive Adventures, said he was amazed at the success of the operation in the Tham Luang cave, which, as of Tuesday afternoon, had seen eight boys brought to safety.

Rescue efforts continued yesterday to retrieve the remaining four boys and their 25-year-old coach.

Mr Fitzgerald, who has decades of diving experience and more than 4000 dives under his belt, understood more than most the complexities of bringing the team out alive.

He hoped the final group would make it to safety and was in awe of the rescue mission.

“(The rescuers) have done extremely well. Teaching somebody to dive is a challenge and cave diving in itself is a pretty big, daunting task,” Mr Fitzgerald said.

“To get a group of young kids who have never dived before, to teach them to dive inside a cave and go into water where there is zero visibility, with fast-running water and doing something your body is not used to doing, is a whole new experience.”

Mr Fitzgerald said his concerns rested with the welfare of the coach.

“I think their biggest challenge is going to be the coach, as the the kids have no fear factor,” he said.

“It’s the adults who have more fear if something were to go wrong.”

He said cave diving was one of the most challenging types of dives, usually left in the hands of the most experienced.

“Cave diving is extreme – you need to be very experienced,” he said.

“You should have at least 50 dives up before you even think of doing a cave dive.

“A lot of people die in caves.”

Unfortunately, the Thai soccer team did not have the luxury of previous experience.

With limited training and the complex profile of the cave, the risks were particularly heightened.

“The biggest danger is, if one of the kids panics – and the kids are going to be anxious for a start – things can go wrong so fast,” Mr Fitzgerald said.

“Anxiety plays a part in most divers. I’ve called off dives in the past due to anxiety, but these kids don’t have that choice. They have to get out of there.

“If they rush to the surface, they have the risk of decompression illness (known as ‘the bends’).”

He said teaching amateur divers to breathe underwater was a big ask, especially those with limited water confidence.

“A tank of air, for me, will last an hour and a half. These guys have never dived before and they're going to be breathing like no end,” he said.

“The biggest fear is how much air they’re going to use and how many tanks they have spare.”

Mr Fitzgerald congratulated the rescuers, which included six Australian Federal Police divers and one Australian Navy diver.

“It’s a fantastic job by the boys and they have planned it so well,” he said.