White Island Tours is very professional and takes safety seriously, the company's auditor says.
Police are investigating on behalf of the coroner, and WorkSafe is carrying out a separate investigation.
Read more on the Whakaari/White Island eruption:
- Whakaari/White Island eruption: a timeline of 9 December
- The dead and the missing
- Police will continue their ocean search but admit bodies may never be found
- WorkSafe ambiguity 'really unhelpful' - Paul Quinn
Adventure safety certifier AdventureMark has carried out a three-yearly audit of White Island Tours in 2017, and another two surveillance audits since then.
AdventureMark director Hemi Morete said the only non-conformities they found were minor and did not affect safety. He declined to identify the non-comformities or whether they were resolved.
"We've got a lot of clients who have a lot more serious issues that this operator ... they are a very professional outfit and we've had no cause for us to be concerned with the way they are operating."
Morete said AdventureMark did not seek independent advice on volcanic threats for its audits but was "guided by" updates from GNS Science, including its threat levels for Whakaari/White Island.
Police are continuing to search for the bodies of tour guide Hayden Marshall-Inman and 17-year-old Australian tourist Winona Langford, who they have named as the two people still missing after the eruption last Monday.
Bad weather and ashfall near the island have confounded search efforts for the past couple of days.
Meanwhile, the likelihood of further eruptions on Whakaari/White Island is continuing to drop.
GNS Science said there was now a 20 to 40 percent chance of eruption over the next 24 hours, compared to 50-60 percent chance a few days ago.
It warned however that an explosive eruption from the main vent area remained possible and could still happen without precursor activity.
Wet weather has meant some of the ash has been cleared from solar panels and monitoring equipment on the island, and solar charging is under way again.
Scientists have been able to monitor the volcano using the remaining equipment on the island.