POLICE in New Zealand have said a sixth person has died following the eruption on volcanic White Island.

A statement said the person was being treated at a local hospital but did not confirm their nationality.

"Police can confirm a further person has died following the eruption on Whakaari/White Island, bringing the official toll to six," the statement said.

"The person was earlier being treated at Middlemore Hospital.

"Police remain focused on supporting families at this terrible time."

Earlier it was confirmed two British women were in hospital after the eruption, with at least eight others missing and feared dead.

As horrific details emerged about the eruption – in which most victims suffered severe burns – police confirmed that officers are investigating the incident on behalf of the coroner.

The probe will run parallel to an inquiry by WorkSafe New Zealand. It was earlier suggested there would be a criminal probe, but officers later said it was too early to confirm this.

White Island, off the country's North Island in the Bay of Plenty, erupted with a large plume of ash and jets of scalding steam on Monday while dozens of people were exploring New Zealand's most active volcano.

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It is believed most of the 47 people on the island at the time of the eruption were from Australia.

Conditions on the island remained too dangerous for rescue workers to attend, but officials said flyovers had revealed no signs of life.

Prime Minister Jacinda Ardern told parliament the "scale of this tragedy is devastating".

"We know, too, there will be bigger questions in relation to this event. These questions must be asked and they must be answered," she said.

"But our focus now is on discharging our duty of care to support those affected and that is also the focus of the police."

The UK High Commissioner to New Zealand, Laura Clarke, confirmed that two of the 31 people still in hospital are from Britain. It was not clear if more British tourists had been affected.

"We are supporting the family of two British women who have been hospitalised in New Zealand," Clarke tweeted.