Streching from Mayor Island in the north to the tip of the East Cape you will find diving on wrecks and around an active volcano.
Whakaari/White Island is situated 48 km from the east coast of the North Island of New Zealand, in the Bay of Plenty. It is one of the four islands in the Olive island chain. The nearest mainland towns are Whakatane and Tauranga. The island is roughly circular, about two km in diameter, and rises to a height of 321 m above sea level. However this is only the peak of a much larger submarine mountain, which rises up to 1600 m above the nearby seafloor. This volcano has some of the most spectacular views in all of New Zealand.
Whakaari is an active andesite volcano. Its eruptions have produced both lava flows and explosive eruptions of ash. It is New Zealand's only active marine volcano and perhaps the most accessible on earth, attracting scientists and volcanologists worldwide as well as many tourists.
Some content from Wikipedia
Astrolabe Reef , Homestead Reef , Laison's Reef , Lottin Point , Orongatea Bay , Taioma , Taupo , Tuhua Reef , Volkner Rocks