Australian cave diving record set in Tasmania's south, the culmination of generations of exploration

At the same time, the team confirmed a passage between Australia's deepest cave, Niggly Cave, and the fourth-deepest, Growling Swallet Cave system, about 395 metres below the surface.

The Southern Tasmanian Caverneers spent four days camping underground in Mount Field National Park and emerged on Sunday having completed the daring feat and exploring kilometres worth of new passages.

Mr Fordyce said connecting the two cave systems was the culmination of generations of exploration by cave divers.

"It threw a few curve balls and there were a couple of points where it wasn't obvious where it went, a few low flat sections that I had to squeeze through, and a section that I had to walk over with my dive gear," he said.

Tasmanian cave diving: Traversing the unexplored underworlds of Tasmania's caves

"We knew there was a fair bit of water going through so there was a chance a person could fit through."

Mr Fordyce left guidelines on the far point of the Growling system four years ago, and around Christmas last year they found a section on the Niggly side that appeared to run in a perfect line between the two.

All it needed was for someone to dive the Niggly side and connect the guidelines together.

Mr Fordyce swan 200 metres across and a total of 12 metres down to reach the other end, which was 500 metres away from the start at the Growling end. He hoped to complete the 700-metre dive in the future.

Mr Fordyce said there was always more exploration to complete and the team looked forward to their next significant dives.

"It's a pretty lonely, nerve-wracking experience," he said.

"Often it's zero visibility within seconds when you stir up the silt.

"But it's all about exploration. The cool thing about cave diving is that there's no shortcut, you can't take a helicopter there, you can't get a satellite picture, you have to go there to prove it exists.

"It's an obstacle course down there."

The caves are part of the Junee-Florentine system, which contains archaeological sites of extinct megafuna, ancient sediments from the glacial periods and unique cave-adapted fauna species.

It has more than 600 caves and at least 50 kilometres of explored passages, but there is still plenty more to see.

Southern Tasmanian Caverneers president and cave scientist Stefan Eberhard said cave exploration both improved scientific knowledge and informed environmental protection.

"Exploration of these caves is far from complete and much more of this complex and extraordinary puzzle remains to be discovered and mapped by speleologists and cave divers for years to come," Dr Eberhard said.

A documentary is being shot focusing on the Junee Master Cave. Watch a preview here.