"This deeply tragic event was unexpected, but that does not mean it was unforeseeable," he said.

The investigation did not include the rescue and recovery operation — the focus was on the events leading up to the eruption.

"The victims — both workers and visitors — all had a reasonable expectation that they could go to the island knowing that those organisations involved had done all they were required to do to look after their health and safety. But had they? That's the question WorkSafe was mandated to investigate."

While Parkes wouldn't name those charged, Prime Minister Jacinda Ardern said two government agencies, GNS Science and the National Emergency Management Agency (Nema), were among the 10 organisations.

She said it was an independent decision taken by WorkSafe.

Her message to the families affected was that all Kiwis' thoughts were with those who experienced loss or injury.

Mark Inman said the charges were not what his brother, tour guide Hayden Marshall-Inman, whose body was never found, would have wished. His employer, White Island Tours, is one of the companies charged.

"He would be hugely disappointed in the fact that potentially some of his friends have been charged. They all did the best of their ability and ran a professional outfit at Whakaari/White Island and for him to find that out he would be hugely disappointed," Inman told TVNZ.

But the charges have provided "some relief" to Meredith Dallow, whose twin, Gavin Dallow, died with his 15-year-old stepdaughter, Zoe Hosking. His wife, Lisa, 48 was critically injured, suffering burns to almost 60 per cent of her body.

"I'm not surprised there have been charges laid and I'm actually quite pleased to be honest," said Meredith.

She was only guessing who had been charged at this stage, but the maximum fine of $1.5 million for each group was "better than nothing".

"I'm glad the WorkSafe investigation went ahead and there is an outcome but it doesn't really put closure to things," she said from Adelaide.

She believed closure wouldn't come until the court cases and coronial inquest were over, but she was thankful the WorkSafe findings were released now rather than next week, around the anniversary of the eruption. "It does give us some relief, especially as we come close to the 12-month anniversary.

The Whakaari/White Island eruption on December 9 last year claimed 22 lives. Photo / Michael Schade

The three people charged as directors or individuals, who were required to exercise due diligence to ensure the company meets its health and safety obligations, face maximum fines of $300,000.

Gavin's father, Brian Dallow, says he can't understand why the three individuals can only be fined $300,000 — if they were that neglectful to health and safety standards a jail sentence would be appropriate.

Steve Milbank, whose son Jake Milbank, 19, will need treatment for the rest of his life after suffering burns to 80 per cent of his body, said news of the charges didn't reveal much.

WorkSafe wouldn't identify the 13 parties, saying they needed an opportunity to go before a judge to apply for name suppression.

Milbank said it would be a long time before details of why they were charged would be known and the report's release was only the first stage. "We're not going to know anything for a while yet."

Volcanic Air pilot and director Tim Barrow said the company was not sure of the nature of the charges it was facing but once notified would take time to seek legal advice.

White Island Tours is facing two charges of breaching the Health and Safety at Work Act but couldn't comment any further about them given the legal process was ongoing.

Paul Quinn, chairman of Ngāti Awa Holdings, which owns White Island Tours, said the iwi expressed its heartfelt condolences to the families at the time of the eruption that lost loved ones. "We continue to include them in our prayers. Similarly to the survivors, we continue to offer our love and support."

A court date is scheduled for December 15 at the Auckland District Court.

White Island is owned by the Buttle family, through Whakaari Management Limited and its three directors, James, Peter and Andrew Buttle. Their lawyer confirmed last night they had been charged but had yet to receive specific details.

Whakaari Management Limited granted licences to the operators that undertook tours to the island.