A Defence Force mine disposal exercise has turned into the real thing after Navy divers discovered four World War II mines off Auckland's coast.
The Navy says the unexploded mines were found on Thursday by Japanese and United States navy divers taking part in an international exercise north of Auckland.
Lieutenant Commander Trevor Leslie, who commands New Zealand's navy dive squad, said the mines are in about 30 metres of water near Tiritiri Matangi Island.
He said the mines were built to last and are in good condition, so New Zealand divers are now checking them to see if they pose a risk.
Lieutenant Commander Leslie said divers used a small charge to open up one of the mines underwater on Thursday. That mine was safe so it will remain on the sea floor but if any of the others is at risk of exploding, divers will deactivate it and bring it to the surface.
He says the mines are among 1400 defensive mines that New Zealand troops laid around the coast during World War II.
There are also nearly 300 mines laid by enemy forces in New Zealand waters during the war. The work will take about a month.