One expert has warned Aucklanders should be prepared for the chance of a volcanic eruption.

Civil Defence estimates there's a 10 percent risk it could happen in the next 50 years. 

It could cost $65 billion in building damage alone. 

Victoria University's Dr Finn Illsley Kemp says we'd get a decent warning before an eruption - but every aspect will be expensive, including evacuating the city.

"We do think we'll get a warning when it is on the way, because this magma has to come from quite deep - we should be able to see it when it's on its' way, but when it's on the move, it doesn't hang around."

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