A 2018 photo of Whakaari/White Island owner James Buttle, taken from his open Facebook profile page.

A spokesman for the owners of Whakaari/White Island says his family was shocked by Monday's devastating eruption and their thoughts were with the people affected by the tragedy.

While it is a scenic reserve regularly visited by the public, the island has been privately owned by the Buttle family since 1936 when it was bought by Auckland stock broker George Raymond Buttle. It remains in possession of the Buttle family under the Whakaari Trust.

At 2.11pm on Monday New Zealand's most active volcano erupted while 47 people were on it. At least six people are confirmed dead, eight others are missing, presumed dead, and 30 people are being treated in hospitals across the country.

In a statement on Tuesday evening, Whakaari Trust spokesman Peter Buttle said their thoughts were with those affected by the tragedy.

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"That we now have had a tragic event with devastating consequences leaves us absolutely heartbroken," Buttle said.

FACEBOOK A photo of Whakaari/White Island owner Peter Buttle, uploaded to his open Facebook profile page in 2016.

The family asked that a rāhui placed on Whakaari be respected.

"We wish to thank everyone involved in the rescue effort, including the first responders, medical personnel and the locals who helped evacuate people from the island.

"Their efforts have been both courageous and extraordinary."

AUCKLAND RESCUE HELICOPTER TRUST Whakaari/White Island as seen from the air following a major eruption on Monday afternoon.

The family turned down an offer by the Government to buy Whakaari/White Island in 1953. Instead a compromise was reached to make it a private scenic reserve, a status which stands today.

The island was later passed on to Buttle's son, John.

It is now owned by Whakaari Trust, which is managed by Whakaari Management Limited, made up of three directors Peter, James and Andrew Buttle.

TOM LEE/STUFF New Zealand Prime Minister Jacinda Ardern briefs the media Tuesday morning following the eruption of White Island, killing at least 5.

Its most recent listed valuation was in 1998 when it had a rateable value of $75,000.

Access to the island is restricted to a few tourist operators who take visitors on boat and flight tours.

One of those, White Island Tours, which was acquired by Ngāti Awa Group Holdings in 2017, owns a fleet of boats which operates daily tours to Whakaari/White Island.

STUFF White Island Tours chairman Paul Quinn says it took nearly 18,000 visitors to White Island in 2018.

Ngāti Awa Group Holdings is the commercial arm of Te Rūnanga o Ngāti Awa - the entity that manages the collective affairs of the members of Bay of Plenty iwi Ngāti Awa.

White Island Tours' website has been shut down, featuring nothing but a landing page that says "We are currently experiencing an emergency" and listing contact information.

White Island Tours chairman Paul Quinn told TVNZ on Tuesday morning two of its staff were unaccounted for following the eruption.

"We take our health and safety responsibilities very seriously and this is a big tragedy unfortunately for us," Quinn said.

In 2018 it took 17,500 visitors to the island, he said.

It received reports from New Zealand Crown Research Institute GNS on what volcanic activity levels were on the island, he said.

It was deemed safe for tours to operate if it was at "level two" or below, as it was yesterday, subject to weather, he said.

"We take our steer from GNS on that."

Whakaari/White Island had been at level one in October when increased volcanic activity levels were recorded at the island.

It had been at level two for about a week before the eruption, Quinn said.

"We need to regroup and provide our support to those most affected."

A White Island Tours press release issued on Monday said it was deeply saddened following the eruption.

"Devastation is an understatement. This is a terrible tragedy and our thoughts and prayers are with everyone who has been impacted," Quinn said.

White Island Tours were assisting police and civil defence with the official emergency response.

"We acknowledge the considerable efforts from police and civil defence and will continue to do whatever is necessary throughout the rescue operation," Quinn said.