White Island volcano, off the Bay of Plenty coast, has erupted for the second time in a week to a level that would have put anyone on the island at risk.
GNS Science says a moderately explosive eruption, lasting about a minute, occurred at 8:09pm yesterday.
It spread an ash cloud column and new mud across the main crater floor, according to camera images from the crater rim.
The latest eruption has prompted GNS to raise the volcanic alert level to two, and the aviation colour code to orange.
It says the latest eruption is larger than other recent events, and would have been life-threatening to people on the island.
The event follows a 15-minute eruption on Tuesday afternoon, with an eruption of steam and mud generating a steam plume that may have been visible from the mainland.
Following that eruption, GNS raised the aviation colour code warning from green to yellow, but kept the volcanic alert level at one.
GNS says the activity is a continuation of 15 months of unrest from the volcano, with hazardous eruptions occurring with no warning.
Volcanic tremor levels have been elevated since September 24, but are lower than those during eruptive activity earlier in the year.
The island is an uninhabited private scenic reserve with boat tours running daily from Whakatane.
Visitors require permission to land on the island, and tours are usually suspended following heightened activity.