A Hamilton man who gave first aid to some of those critically injured says he poured cold water over their severely burned bodies and kept talking to them to stop them losing consciousness as the tour boat made a desperate return to shore.
Geoff Hopkins told Checkpoint he had just finished his tour of the volcanic island in Bay of Plenty when the eruption occurred.
"[We] were just having a little tour around some of the bays just a few hundred metres offshore when it erupted.
"It was very quiet, but there was definitely an attention-grabbing moment… everybody on the boat turned around and we could see the eruption.
"It was just a big, beautiful cloud that was rising, that was white and grey. For a second it kind of just grabbed your attention. And then seconds after this menacing rolling cloud of ash just rolled over the cliff and headed out and down to sea.
"We were all ushered inside the cabin of the boat and the boat took off pretty quick."
He said they could not see the second tour group on the island at that point.
"As we as we got inside the boat and went back around the other side you couldn't see the island at all. The island was just completely covered in in falling ash."
The boat he was on returned to help pick up people remaining on the island.
"We went back to where we had left, to where the other boat has been anchored," he said.
"At that stage the ash had cleared. We could see clearly on the island there were some people in the water… and the inflatable started picking people up and bringing them back to our boat.
"There was a call for doctors. We indicated we were first aiders… we went out to help, and pretty much everybody that was coming on was with significant burns."
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A few people were grey over most of their body, but most people had ash on their faces.
"I can still smell the ash on my hands. I can't get it off, the smell must be stuck into everything."
Hopkins said he saw burns on exposed skin - arms, legs, faces - but the most critically injured were those who had been burned through their clothing.
"We just started to treat burns. We had a lot of fresh water on board, we were able to use fresh water, we just called out for any containers that we could use. And we got people to start filling them up, just starting to pour cool, fresh water over people's burns. The more critical ones we needed to remove closing and wrap them up.
"I was just busy treating people so I'm not sure what the trigger was for us leaving, but we started heading back. About halfway back we met a coastguard boat, who put two paramedics on board and they were able to assist but there was not a lot they could really do, just a bit of pain relief.
"The two people that I was with, we couldn't get a vein to get anything into them intravenously."
Hopkins said he had never faced anything like it before - he was helping to treat US newly-weds Matthew and Lauren Urey, who had critical burns.
"They were in an out of consciousness, so just really just trying to keep them alive until we could get them to shore… A lot of talking to them, a lot of reassuring.
"My daughter treated someone with a head injury. But we believe that was from a fall. There was nothing to suggest anybody had been hit by anything.
"The tour boat from that second group that were on the island was still there. We left behind our inflatable with I think one of our crew, maybe two of our crew stayed behind. And they came back on the second tour boat. I think they came back about half an hour after us."
Initially he thought people's burns were caused by hot ash, but he was not certain.
"People were burnt underneath their clothing and their clothing looked fine.
"You'd lift someone's shirt, and the shirt was in perfect condition, but there would be terrible burns underneath it. So yes, potentially steam."