The first eruption in over 100 years at Mt Tongariro may spark months, weeks or even years of volcanic activity - but poses no immediate risk to the community.
Mt Tongariro rumbled into life at 11.50pm last night, sending ash and rock a kilometre into the air and across roads, prompting a potential threat warning for central North Island regions.
The "small scale" eruption was a total surprise, GNS volcanologist Michael Rosenberg said.
It threw rocks and spewed ash from the Te Mari craters, near Ketetahi hot springs, on the northern side of the mountain, GNS Science said.
Five to 15 milimetres of ash blanketed nearby properties.
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