Four World War II mines have been discovered on the seabed during a Navy exercise in Auckland's Hauraki Gulf this week.
Two were discovered during a routine Autonomous Underwater Vehicle (AUV) operation conducted by the US Navy as part of the international Mine Countermeasures Exercise hosted by the Royal New Zealand Navy.
The discovery was confirmed by a New Zealand navy dive team.
Two more mines were discovered by a Royal Australian Navy AUV team and later confirmed by Japan's dive team.
The four mines were originally laid as part of a controlled defensive minefield in September 1942.
Seven loops totalling 16 mines were laid as part of a larger defensive manoeuvre which saw 1391 friendly mines laid in 10 harbours across New Zealand.
At the end of the war most mines were disposed of using mine sweepers, however some 50 sank to the bottom, irrecoverable until new technology was available.
The Navy advises that due to their age and condition any remaining World War II mines are unlikely to be dangerous.
However, they recommend caution if divers find one. It is recommended that any discovery be reported to the Harbourmaster or Royal New Zealand Navy.