An emergency management plan for a Whakaari/White Island eruption had not been finalised when the volcano erupted on December 9.
The Bay of Plenty Civil Defence Emergency Management Group had an "operational draft" response plan in place on December 9 which was "the effective response framework" at the time.
The draft's "Search and Rescue Plan" was two sentences long, on the final page.
"In the event of a mass casualty occurrence on the island, the New Zealand Police will lead the co-ordination of any rescue operation to bring them back to the mainland for treatment.
"The Bay of Plenty District Health Board will support the police in the search and rescue effort providing triage and treatment facilities as will the Bay of Plenty CDEM Group in providing emergency welfare support where required."
Emergency Management Bay of Plenty director Clinton Naude said search and rescue was the responsibility of New Zealand Police and was led by police after the eruption.
He said the response plan was "under review at the time of the eruption and in the final stages [of] approval".
"The response plan details internal operational functions to be carried out by Emergency Management Bay of Plenty."
He said it was used in the early stages of the eruption response in December.
"It supported response staff to understand roles and responsibilities."
The regional council's general manager of regulatory services, Sarah Omundsen, said: "The response plan assumes that other key agencies have their own response plans and/or management processes."
The information about the plan was obtained from the Whakatāne District Council and Bay of Plenty Regional Council by NZME under the Official Information Act.
The plan said the most significant risk to the public at the island was "an explosive event".
There were more likely to be "precursors" - warning signs - of a large event than a smaller-scale event, but either could hurt or kill people.
"Therefore, when people are in the vicinity of Whakaari/White Island volcano there always exists some risk of death or serious injury to those people."
It said all operators were aware of the risks and managed them by regularly communicating with GNS and each other with observations from the island, giving visitors gas masks and hard hats, daily assessments of the volcanic activity and risks, and using the personal experience and judgment of their own staff.
The plan said GNS' role was to "provide the best possible scientific advice".
It said if the civil defence group felt the risk to the public was too great for visitors it could restrict access in consultation with agencies and tour operators.
The Bay of Plenty CDEM led the response to the December 9 eruption and the National Emergency Management Agency supported this by co-ordinating the initial all-of-Government response.
The emergency management group is governed by a joint committee of Bay of Plenty mayors and an elected member of the Bay of Plenty Regional Council.
Whakaari's distance offshore means it does not come under the authority of any city or district council.
In August 2017, a Memorandum of Understanding was signed by the Associate Minister of Local Government Jacqui Dean and the group.
At the time, the Bay of Plenty Regional Council said the emergency management group would "work to ensure people are ready and able to respond to an emergency on Whakaari/White Island".
At the time of the signing, the group's joint committee chairman, former Tauranga mayor Greg Brownless, said the members would "continue working with those who visit and use the island ... to ensure the readiness and response planning they did was adequate for the risks the island presented".
On December 9, victims of the eruption were evacuated by one Westpac Rescue Helicopter, two Kāhu NZ helicopters and one from Volcanic Air which all landed on the island after the eruption to help survivors, most of whom had burns and respiratory injuries.
Others were triaged on the boat Phoenix on its way to Whakatāne Wharf where a cordon and further triage and staging area was in place.
So far 21 people have died from their injuries at White Island, two of whom died in Australia where they had been transported for care, according to a Ministry of Health update on February 3.
Seven patients remain in hospital in New Zealand, one of whom is in a critical condition.
Four are in Middlemore Hospital, two in Waikato Hospital and one in Hutt Valley Hospital.