On Tuesday afternoon, police announced a criminal and workplace investigation would be conducted into the circumstances of the deaths on White Island.

They later backtracked and said it was "too soon" to assess whether a criminal investigation would take place.

Regardless of whether it does, Australians and Kiwis alike are asking themselves just how this tragedy came to be.

As of Tuesday afternoon, five people are confirmed dead, with a further eight trapped on the island during the blast and assumed to have died.

Medical officials have also warned of the possibility of further deaths in the nation's hospital units, where all but a handful of 31 affected patients are in a critical condition.

The wait to confirm the health, the names and nationalities of those involved has brought trauma to families and friends of those involved in the blast.

Police believe 47 people, from seven countries, were present during the eruption.

Ardern said grief-stricken loved ones deserved to know the truth behind the "devastating tragedy" but that needed to wait for the recovery process and recuperation of the injured.

"We know too there will be bigger questions in relation to this event," she told parliament.

"These questions must be asked and they must be answered.

"The New Zealand police are quite rightly focused on supporting the recovery operation ... (and) our focus is on discharging our duty of care to those affected."

Deputy Commissioner John Tims confirmed that 24 Australians were among the 47 near the volcano at the time of the blast, without specifying whether they were among the dead, trapped, injured or discharged.

There are also nine Americans, five Kiwis, four Germans, two Britons and Chinese and one Malaysian involved.

Full details of the conditions of those on the island during the blast will only be known after the recovery operation.

Police are unwilling to sanction a return to recover bodies until they can guarantee the safety of emergency services workers to set foot on Whakaari.

While the blast has many questioning the appropriateness of tourism operations on the island, mayor Judy Turner said she believed the primary tour provider, White Island Tours, to be responsible.

"Personally I've been out with them and was very impressed with the briefings that were given and the attention to health and safety protocols that were done," she said.

"I'm very confident that they can be safe practitioners.

Turner believes they acted conscionably by taking a tour on Monday.

"At the time they went out that was a level two. That wasn't considered in the matrix of things a high reading," she said.

Australian Associated Press