New Zealand might be known as Australia's smaller neighbour but scientists have discovered it is sitting on a previously unknown continent - Zealandia.

It is 94% under water but meets all the criteria applied to Earth's seven other continents, say researchers.

The 1.9 million-square-mile land mass includes New Zealand's North and South Islands, as well as New Caledonia and several other territories and groups of islands.

It was once part of the Gondwana super-continent but broke away about 100 million years ago.

"The scientific value of classifying Zealandia as a continent is much more than just an extra name on a list," says the study in the Geological Society of America's journal, GSA Today.


"That a continent can be so submerged yet unfragmented makes it (useful)... in exploring the cohesion and breakup of continental crust."

Lead author Nick Mortimer said scientists had spent more than 20 years gathering data to make the case for Zealandia.

Their task was difficult because most of it is hidden beneath the waves.

"If we could pull the plug on the oceans, it would be clear to everybody that we have mountain chains and a big, high standing continent," he told TVNZ.

"What we hope is that Zealandia will appear on world maps, in schools, everywhere," he said. "I think the revelation of a new continent is pretty exciting."

Previously, New Zealand and New Caledonia were grouped with Australia in Oceania.