The Workplace Relations Minister has confirmed White Island Tours, which took tourists to the island on the day of the eruption, was audited in recent months.
WorkSafe's chief operating officer would not give details on audits of the company but Iain Lees-Galloway said two surveillance audits had been done in the past two years.
Lees-Galloway said a three-yearly audit was done in 2017 and two surveillance audits had been done since.
However, he said, "there is a question there about whether or not the adventure activity regulations are fit for purpose and I think it's a question that needs to be answered."
Two inquiries into the tragedy are under way, one by police on behalf of the Coroner and the other by WorkSafe, as is mandatory when a death occurs at a workplace.
WorkSafe chief operating officer Phil Parkes said it would investigate whether rules were fit for purpose.
He said just being on the island didn't qualify as adventure tourism under current regulations.
"The travel to and from the island would have been covered by transport regulations, helicopters will be registered with CAA, boats will be covered by Maritime [NZ].
"Depending on what the activity would have been on the island would determine if that was an adventure activity or not," he said. "There has to be a workplace, paid activity. The operators have to be providing some sort of guiding during that episode.
"If the operator was taking people to the island and providing guided tours then that would be covered by the regulations."
White Island Tours says it is classified as an adventure tourism operator. "As part of this, our safety procedures are audited to ensure that our Safety Management System complies with the relevant standards.
"The most recent audit was conducted by Adventure Mark, who are accredited by WorkSafe to undertake this task, in August 2019."
Prime Minister Jacinda Ardern said WorkSafe would be reviewing its regulatory framework. "Did the operators fulfil the expectations around health and safety audits and so on?
"The question may well be, was that regime itself adequate and did WorkSafe do their job?"
Ardern said WorkSafe couldn't look into it and she was looking for more advice.
Parkes said employers had the obligation to look after their workers and people in their care.
"There's an additional layer of regulation specific to adventure activities. For those regulators, they have to go on the register and there's a third-party audit company that looks at the safety procedures.
"WorkSafe doesn't directly audit their activities."
Parkes said only one company, White Island Tours, was on the register at the time of the tragedy.
The helicopters weren't on the register. There had been ongoing discussions between WorkSafe and the companies. That would form part of the investigation, he said. "Our position has been for the past two years that there were some operators who were taking trips to the island that should've been registered."
He said differing views on the regulations had brought discussions to a stalemate.