Four World War II mines have been found on the seabed off Whangaparaoa peninsula, north of Auckland.
The first two mines were discovered by a United States Navy Autonomous Underwater Vehicle during the multi-national Mine Countermeasures Exercise in the Hauraki Gulf.
New Zealand Navy divers confirmed the discovery.
An Australian underwater vehicle discovered two more mines and a Japanese team of divers confirmed the find.
A Navy spokesman said the four mines were laid in September 1942, part of a series of 1,391 mines which were laid across 10 New Zealand harbours.
Mine sweepers cleared most of the mines but about 50 sank and were irrecoverable.
The Navy said the remaining mines were unlikely to be dangerous but if any recreational divers came across them they were advised to exercise caution and report the mines to a harbour master or the Navy.
- Fairfax Media