New Zealand's claim over 1.7 million square kilometres of seabed has been confirmed by a United Nations commission.
The continental shelf is the area of seabed outside New Zealand's existing 200-nautical-mile exclusive economic zone.
Recognition of the new continental shelf boundaries will enable New Zealand to exercise its rights to the area, including exploiting resources such as minerals and petroleum.
Prime Minister Helen Clark says New Zealand's submission to the UN was the result of a $44 million project carried out by officials and scientists.
The seabed area is six times the size of New Zealand's land mass.
The UN agreement gives New Zealand the rights to resources on or under the seabed, but not to those - such as fish - in the waters lying outside its exclusive economic zone.
"This success enables New Zealand to exercise its rights to the continental shelf with certainty, including its rights in the future, if it chooses to pursue them, to resources such as minerals and petroleum," Miss Clark says.
A continental shelf boundary with Australia has already been agreed, although other boundaries with Fiji and Tonga to the north are still to be finalised.
New Zealand is the fifth country to make a submission to the UN Commission on the Limits of the Continental Shelf after Russia, Brazil, Australia and Ireland.