An elite team of cavers from the Southern Tasmanian Caverneers discovered the cave - which has been named Delta Variant - on Saturday, after 14 hours underground and following six months of preparation.

It is connected to Tasmania's Niggly and Growling Swallet cave system, northwest of Hobart.

"I was definitely nervous, you feel aware of your own mortality," team member Ciara Smart said.

"Although you know you're safe, it's very intimidating and the sound as well - it's a constant roar of the waterfall. You can't hear anything above your own breath, it's scary at times."

The cave was named after a COVID-19 variant "to remind future cavers of contemporary events".

The team entered the cave about 11am on Saturday and emerged at about 1.30am on Sunday.

They faced challenging conditions underground due to high water levels.

"The cave was exceptionally strenuous," caver Ben Armstrong said.

"It was extremely vertical, requiring hundreds of metres to be ascended and descended on ropes."

The cave lies metres away from the entrance to the Niggly System, which was discovered in 1994 and at 397 metres was previously the country's deepest known cave.

Australian Associated Press