The New Zealand authorities on Tuesday declared Kermadec region, an area of the South Pacific about the size of France, as a new marine reserve.
The 620,000 sq.km sanctuary is about 1,000 km north-east of New Zealand, Radio New Zealand reported.
Prime Minister John Key made the announcement at the UN General Assembly in New York.
Fishing and mining will be banned in what Key called "one of the most geographically and geologically diverse areas in the world."
"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," he said.
Also Read
The area concerned is one of the most geologically diverse marine habitats in the world and serves as a breeding and feeding ground for a variety of marine mammals, fish and invertebrates, including dolphins, turtles and coral.
It is home to the world's longest chain of submerged volcanoes and the second deepest ocean trench, with a depth of 10 kilometres.
WWF New Zealand chief executive Chris Howe said it was a major achievement and testament to many years of hard work by thousands of New Zealanders.
Environment Minister Nick Smith said the sanctuary, which is 35 times bigger than all New Zealand's 24 marine reserves added together, "will be a large area in which nature rules."
"It's part of that global effort for us to lift our game in managing the oceans of the world," he said.
Smith said the sanctuary would be monitored by the navy and satellite technology.