Mt Tongariro is one of three major volcanos in the central North Island, sitting alongside mounts Ruapehu and Ngauruhoe.
The mountain has been dormant for 115 years - the last series of eruptions began in November 1896 and lasted until October 1897.
According to GeoNet, Tongariro is a complex of multiple volcanic cones constructed over a period of 275,000 years.
The mountain's active vents include Te Maari, Emerald, North Crater and Red Crater.
Seismic activity indicating unrest was last detected at Mt Tongariro during 2001.