"Distressing" images of the Whakaari eruption from GNS Science webcams are forming part of WorkSafe's multimillion-dollar probe.
The investigation into the December 9 eruption that killed 21 people, including two White Island Tours guides, is WorkSafe's biggest to date.
It has cost $1.7 million so far but up to $4m has been set aside.
Both the police and WorkSafe have access to livestream video from the afternoon of the eruption, captured by GNS Science's webcams.
GNS uses round-the-clock live camera footage to monitor New Zealand volcanoes, including Whakaari/White Island.
Documents released to NZME under the Official Information Act show GNS shut down public and internal access to the livestreams at Whakaari out of respect for victims and their families, and to protect the wellbeing of staff.
The institute sought volunteers willing to review footage during the recovery of bodies from the crater floor, to minimise "psychological injury" to others.
In a statement, GNS' acting chief executive Andrew Simpson said: "Limiting the access to these images was the right thing to do in the circumstances."
Another media spokesman also said the institute had "shared all video of the eruption with WorkSafe", and police first accessed the footage to help the recovery operations.
Forty-seven people were on the island at the time of the eruption.
GNS uses round-the-clock live camera footage to monitor New Zealand volcanoes, including Whakaari/White Island.
WorkSafe's investigation is expected to take a year.
The health and safety regulator was established in 2013, three years after the Pike River Mine disaster.
In response to questions this month, WorkSafe was not able to provide specifics of how the Whakaari investigation was being carried out but a spokeswoman said staff had been "stood up" to focus on family and victim liaison and video interview machines were being used.
The regulator has 27 staff working on the case, including four managers who are trained as inspectors, 16 inspectors, along with other specialist and support staff.
Under current legislation, any charges must be laid by WorkSafe within 12 months of the workplace incident - December 9, in the case of Whakaari/White Island.
WorkSafe can prosecute for breaches of the law - penalties and criminal sanctions range from $50,000 to $3m and up to five years in prison.
Police are also investigating the deaths on behalf of the Coroner.
When asked for budgeting and staffing numbers for the investigation, a police spokeswoman said the work was "thorough" and "complex" but police were "unable to comment further".
East Coast MP Anne Tolley told NZME this week: "I would be very disappointed if they were punished for operating in what will always be a very risky environment if the investigation cannot find evidence of negligence or unnecessary risk-taking.
"I think the fact that several of the staff stayed behind to rescue visitors and lost their own lives in the process proves how dedicated the staff were to their tourists."
She hoped the investigation "isn't as traumatic for the operators as I know the tragic events have been".
She said she had been to the island several times "and always understood the risk".
Waiariki MP Tāmati Coffey said as the investigations progressed, "we owe it to all whānau involved, not to focus on hypothetical outcomes that generate unnecessary trauma, but to continue putting people first, united in kindness and aroha".
"Once complete, the Government will consider what, if any, further issues require consideration ... That way, we can ensure that as a nation we learn, and that future generations who call the eastern Bay [of Plenty] home, never have to collectively process such anguish again."
In June, Deputy Prime Minister Winston Peters said the absence of tours to Whakaari/White Island since the eruption, and the Covid-19 pandemic, had a "dramatic effect" on White Island Tours owners Ngāti Awa Group Holdings.
Ngāti Awa bought White Island Tours in 2017 from the Tait family in Whakatāne, who founded the business in the 1990s.
Eastern Bay of Plenty Police revised a lengthy "White Island (Whakaari) Eruption Response Plan" document in 2018 and although in draft form, the plan was in place at the time of last year's eruption.
It was distributed to other emergency services, Bay of Plenty Regional Council, Coastguard, GNS Science, Whakatāne Hospital, Land Search and Rescue and tourism operators, all of whom contributed to the plan.
The 42-page document released to NZME under the Official Information Act catered for "a need to safely remove any persons present who are not able to be evacuated by the tour operators".
It said "when people are in the vicinity of White Island (Whakaari) volcano, there always exists some risk of death or serious injury" but that all operators were "aware of the risks to themselves and customers" when visiting the island and "manage the risk in essentially the same way".
This included regular communication between tour operators and with GNS Science, sending out a guide scout or doing a flyover to assess the island before landing, providing visitors with gas masks and hard hats.
The plan said the "suitable shelter" - a shipping container put on the island in 2016 - would hold provisions such as water and emergency supplies and "act as a safety zone".
It also incorporated the use of rescue helicopters and large triage vessels on which to treat anyone injured.
Attached to the plan was White Island Tours' "emergency evacuation procedure" as of May 2016.
It said guides carried first aid kits and in the event of an emergency they needed to "quickly assess" the type of incident and severity, "ensure no further harm" to victims, be in contact with the tour boats, request back-up if needed and "evacuate island/administer first aid as required".
The procedure said guides would also "take charge and instruct passengers clearly and calmly where to go and what to do" and "keep constant headcounts".
It also said when volcanic activity increased at the island, this information was put on the "front page" of White Island Tours' website, passengers were also given updated safety terms to read, they were reminded of increased risk over a microphone before disembarking the boat and that they could stay on board if desired.
"The first talk on the island is a safety talk and as well as giving instructions on how to use the safety gear, guides also describe the hazards visitors may encounter during their time on the island and the corresponding procedures to follow. This includes eruptions, landslides, excessive steam and hot spots.
"Passengers are reminded during the first two talks to let a guide know if they feel uncomfortable at any stage and want to return to the boat."
Armed police stood guard as the patched members were led out in handcuffs.