Cavers reveal NZ's deepest cave system

Cavers in New Zealand's South Island say they have revealed the southern hemisphere's deepest cave system, which descends 1.2km under Mt Arthur near Nelson.

An expedition to Nettlebed Cave has found a link with the nearby Stormy Pot Cave, expedition leader Kieran McKay says.

Nettlebed, at 889m underground, was previously thought to be New Zealand's deepest cave.

The 150m-long link meant the cave system went about 1200m deep and deeper than the 1123m-deep Muruk cave in Papua New Guinea.

The discovery was made after a seven-day expedition to Nettlebed that finished on Friday.

"We have done it!! Stormy Pot and Nettlebed are now one, we have a cave system 1200 metres deep and the deepest in the southern hemisphere," Mr McKay wrote on his Facebook page.

The seven speleologists had to dig through a rock pile and then squeeze through a narrow gap, only to find themselves in a spot in the Storm Pot Cave that was used as a urinal.

Mr McKay said the discovery was the culmination of many thousands of man hours over 40 years.

Last year, another expedition using dye in the water and smoke, indicated the two caves were connected.

The world's deepest cave is Krubera-Voronja Cave in Georgia, which is about 2200m deep.