John Key has announced that a large area of New Zealand's exclusive economic zone will be turned one of the world's largest ocean sanctuaries.

A vast stretch of New Zealand's exclusive economic zone is being turned into an ocean sanctuary in a landmark deal to preserve one of the most pristine and unique environments on earth.

Prime Minister John Key announced the deal in New York Tuesday NZT, and said it would encompass 620,000 km2 in the seas north-east of New Zealand in the Kermadec region.

"The Kermadec Ocean sanctuary will be one of the world's largest and most significant fully-protected areas, preserving important habitats for seabirds, whales and dolphins, endangered marine turtles and thousands of species of fish and other marine life," Key said.

SUPPLIED Prime Minister John Key with the New Zealand delegation at the United Nations.

The sanctuary will cover 15 per cent of New Zealand's exclusive economic zone, an area twice the size of our landmass and 50 times the size of our largest national park in Fiordland.

"As well as being home to a wide range of marine species, the Kermadec region is one of the most geographically and geologically diverse areas in the word. It contains the world's longest underwater volcanic arc and he second deepest ocean trench at 10 kilometres deep," Key said.

The National caucus was due to be briefed on the move Tuesday. The government is forgoing potentially lucrative mining royalties from turning the area over for environmental protection. However, while there are believed to be significant silver deposits, they are so deep that the logistics of mining in the area would be hugely difficult and also costly.

Among those who have lobbied the Government to protect the Kermadec region are Titanic director and some-time New Zealand resident James Cameron, Hedge fund billionaire Julian Robertson and US Secretary of State John Kerry, who has urged a step up in marine protection world wide.

The sanctuary will create a no-take, fully protected zone preventing all fishing and mining in the area, adding to the protections already in place.

Key announced the deal at the United Nations General Assembly in New York, which has been focused on sustainable development as a critical goal this year.

New Zealand welcomed the focus on the sustainability of the world's oceans and marine resources - a goal which resonated strongly with our own region were so many drew their food and livelihoods from the sea, Key said.

"New Zealanders value our coasts and oceans which are an important part of our culture, economy and environment and we are committed to managing them sustainably."

Green Party environment spokeswoman Eugeanie Sage welcomed the announcement.

"We're delighted the Government has picked up the Kermadec ocean sanctuary concept that has been in a Green private member's Bill drafted by Gareth Hughes several years ago."

But it did not make up for the Government's "poor track record" on other environmental issues.

"We've still got the Maui's Dolphins to protect, water quality to improve, and National is taking an embarrassingly weak proposal on limiting New Zealand's greenhouse gas emissions to the Paris Climate Change Conference."

Environment Minister Nick Smith said oceans were the new frontier for environmental protection.

"They make up 72 per cent of the globe and are home to half of the world's species but currently only two per cent is protected," Smith said.

"There is increased pressure from over fishing, mining and pollution with the populations of fish and seabird species estimated to have halved over the past 40 years."

Just as New Zealand had set aside significant areas of land like the Tongariro and Fiordland National Parks, it also needed to protect special areas of the sea like the pristine ocean around the Kermadec Islands.

According to information supplied by Smith's office, the Kermadec Ocean Sanctuary will be one of the world's largest and most significant fully protected areas. It includes the second deepest ocean trench at over 10 kilometres, deeper than Mt Everest is tall, and an arc of 30 underwater volcanoes, the largest anywhere on earth.

It is also some to six million seabirds of 39 different species, over 150 species of fish, 35 species of whales and dolphins, three species of endangered sea turtles and many other marine species like coals, shellfish and crabs unique to the area.

The new sanctuary will extend to the 200 nautical mile limit of New Zealand's Exclusive Economic Zone from Raoul Island in the north to L'Esperance Rock in the South.

All forms of fishing and mining will be prohibited.

A total of about 20 tonnes of fish are currently caught in the area each year.

The territorial sea around the five Kermadec Islands was established as a 7500 kilometre marine reserve in 1990.