Tour operators could be fined up to $1.5 million, if a Worksafe investigation finds serious breaches of health and safety laws.

That's the maximum fine possible under the Health and Safety at Work Act, with Worksafe investigating the deaths and injuries caused by the eruption on Whakaari/White Island on Monday.

Six people have died since the eruption, including a Kiwi tour guide, a Malaysian national and three Australians, according to Australian media. Eight people were believed to still be on the island.

A Worksafe spokeswoman said a fine could only be imposed by the courts, after a prosecution for breaches of the Health and Safety at Work Act.

That would lead to a prosecution being taken, and, if any breaches were proven, Worksafe lawyers would tell the judge what the agency believed the fines should be, the spokeswoman said.

Other companies also took flights out to the island, and held guided tours.

The safety auditor for White Island Tours said the company was "very professional", and had passed its safety audits over the past three years.

Other companies also took flights out to the island, and held guided tours.

Hemi Morete, lead auditor for AdventureMark, said: "They were a very professional outfit."

To be a registered adventure tourism operator, companies needed to pass a safety audit, and the White Island Tours "Walking on a Live Volcano" activity registration ran until 19 November 2020.

"They passed their audit," Morete said. "I can't go into the details of it now as Worksafe is investigating."

All the audit reports done by AdventureMark had now been given to Worksafe, he said.

The safety audits were not public documents, but Morete said the audits involved scrutinising both White Island Tours' hazard identification and risk management, as well as checking the company was operating in the way they said they were.

But he said the audits were not about eliminating all risk.

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"It's about identifying the risks and managing them. You are never going to be able to eliminate them."

Breaches of the act did not necessarily even have to have been the cause of the injury or death being investigated, he said.

But questions were being asked about whether tourists should have been on the island at the time of the eruption as the "alert" level for the island had been lifted to level 2.

"All that is required is for a reasonable practicable step not to have been taken," he said, regardless of whether it would have prevented the tragedy or not.

Tours of Whakaari/White Island have been running for over 30 years, with around 10,000 a year visiting the island.

But questions were being asked about whether tourists should have been on the island at the time of the eruption as the "alert" level for the island had been lifted to level 2.

The White Island Tours website has been taken down, but just before it was the company explained the risks on its booking page saying: "Whakaari/White Island is currently on Alert Level 2. This level indicates moderate to heightened volcanic unrest, there is the potential for eruption hazards to occur. White Island Tours operates through the varying alert levels but passengers should be aware that there is always a risk of eruptive activity regardless of the alert level. White Island Tours follows a comprehensive safety plan which determines our activities on the island at the various levels."

The company's "current" status on the publicly searchable register meant it had passed a safety audit and was registered and authorised to provide the stated activities for the stated period, Worksafe said.

The requirement to register as adventure tourism operators was brought in by then prime minister and tourism minister John Key after mounting concerns at the number of tourists dying, or being injured, while on holiday in New Zealand.

Work towards cracking down on loose adventure tourism safety began in 2009 following 37 tourist deaths over the previous four years.

A Worksafe report in 2010 on the gaps in adventure tourism safety recommended mandatory safety audits, but while the report listed the kinds of activities that qualified as adventure tourism, it did not mention geothermal or volcanic activities.

Recent prosecutions of adventure tourism operators included that of Riverland Adventures in 2014, which led to a $120,000 fine over the quad-biking death of an Australian tourist.

In 2016, Waikato diving operator Cathedral Cove Dive plead guilty to health and safety failures that led to the death of a Taiwanese tourist in the Coromandel Peninsula in 2014.