The territorial sea is the belt of sea adjacent to the coast out to a distance of 12 nautical miles from prescribed baselines over which New Zealand, as the coastal state, has the same rights of sovereignty that it exercises over its land territory subject to the right of innocent passage (and transit passage through any straits used for international navigation) of ships of other states. 'Innocent passage' excludes fishing activities.
Further References: http://www.linz.govt.nz/hydro/nautical-info/maritime-boundaries
New Zealand has sovereign rights over a vast area of ocean, along with the fishery, mineral and petroleum resources that may exist in that area. The definition of the limits of these waters is a complex task that is undertaken by LINZ in conjunction with the Ministry of Foreign Affairs (http://www.mfat.govt.nz/).