Prime Minister Jacinda Ardern says they are taking things one step at a time.

Thirteen people are presumed to have died, five of those deaths have been confirmed but eight are still missing on the island.

Thirty-one people have been transported to hospitals around the country for specialist care, some of whom have received burns and remain in a critical condition.

Among those caught up in the tragedy are Kiwis and tourists from Australia, the US, the UK, China and Malaysia.

Jacinda Ardern told Mike Hosking the recovery operation is their main priority, but it's a waiting game.

"At the moment we have experts who are providing police with the best information available. Yesterday, experts were pointing to volatility over a 24 hour period."

Ardern has also praised the courageous efforts of first responders.

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