Aucklanders might not have as much time to evacuate in the event of a volcanic eruption as previously thought.
New research by Kiwi volcanologists has found there could be as little as five days between the first detection of activity beneath the city and a devastating blast.
Otago University volcanologist Marco Brenna's team looked at Pupuke on the North Shore, a volcanic explosion crater that's currently occupied by a lake.
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They found when Pupuke erupted 150,000 years ago, it was caused by the arrival of a hot batch of magma arriving from below, more than 50km deep in the Earth.
Once Pupuke's own magma was destabilised by the new arrival, it took between 10 and 30 days to reach the surface.
University of Auckland volcanologist Professor Shane Cronin says current technology wouldn't detect the magma until it was about 27km from the surface - leaving as little as five days for residents to get out.
"This work doesn't change the likelihood of eruptions - but it does change our certainty around how much warning we could potentially have," he told NZME.
Evacuating an area of central Auckland with a 5km radius - about 78 square kilometres - would require moving up to 435,000 people.
The Earthquake Commission is funding research into the effects of an eruption in Auckland, and how the risks can be managed.
Auckland is littered with dozens of dormant volcanoes. Rangitoto is the only one that's erupted more than once, and last blew about 550 years ago.