The discovery was made in the past few days by geologists drilling in the Panmure Basin in Auckland. It is the first volcano to be found in the basin, and is covered by mud and water that filled the area as sea levels rose after the last glaciation.

GNS Science says further tests will need to be carried out, but volcanologist Dr Graham Leonard says the new volcano could be as young as 10,000 years.

Dr Leonard says the Panmure Basin is itself a volcano mouth and it is extremely rare for two eruptions to have occurred at the same site in the Auckland volcanic field.

The GNS website says the Auckland volcanic field has about 50 volcanoes, within an area of 360 square km.

They first began to appear between 60,000 and 140,000 years ago, starting with the eruptions of Albert Park and the Domain. The largest and most recent eruption was Rangitoto, about 600 years ago.