A Hamilton man who gave first aid to those critically injured in the Whakaari/White Island eruption has spoken of the horror.

Boatload after boatload of survivors were pulled onto the man's boat, as those helping poured water over their scalded skin.

Geoff Hopkins, 50, said some drifted in and out of consciousness as he tried to tell them that everything was alright.

He now worries that those he helped are among the dead.

"They were just so massively burnt," he said.

Hopkins had been given the trip to Whakaari for his birthday by his daughter, who' is a geology student. He believes they might have been the only Kiwis on their trip.

After they'd visited the island itself, their boat moved around to get one last look at the crater.

Geoff and Lillani Hopkins who gave first aid to the victims of the White Island eruption. Picture / Lillani Hopkins

"As we turned to start heading back, there was just this gasp across the boat and I looked up.

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"I could just see this plume of white and grey rising quite high and quite quickly," Hopkins told the Herald.

And yet, it was silent.

"At that moment, it was quite beautiful - we were watching a volcano erupt in front of our very eyes.

"But then the ash just rolled up over the rock face and as it rolled over, it just suddenly became quite menacing."

As the ash fell and the blue sky returned, they could see people who'd run into the sea to escape the eruption.

Damaged helicopter is seen on White Island after the deadly eruption. Photo / Instagram

The crew launched the inflatable and rushed over to pull the people out of the water. In the background, Hopkins could see the destroyed helicopter and said it looked like it had been spray-painted grey.

When the first boatload came back from the island, someone yelled: "Is anyone a doctor?"

There were two - one from England and another from Slovenia - while Hopkins, a pastor from Hamilton, and his daughter Lilliani are trained in first aid.

That was when it sunk in how serious the situation was.

The outside decks were used for first aid, while those who'd been on the boat and were unhurt - about 30 - stayed indoors.

Boatload after boatload of injured people were ferried back from the island.

"I don't think there was anyone that came off who wasn't badly burnt."

The only ones who were fairly unscathed were those in the group with the helicopter.

"But where they managed to seek shelter, we don't know," Hopkins said.

"Everyone else was horrifically burnt. People were in shorts and T-shirts so there was a lot of exposed skin that was massively burnt.

"Their faces were massively burnt.

"But there were also huge burns under people's clothes. So their clothes looked fine, but when you cut them off … I've never seen blisters like that."

Tourists are cleared from White Island following the volcanic eruption, Photo / Michael Schade

And then they started screaming in pain, Hopkins said.

There was a lot of fresh water on their boat, so those helping poured as much as they could over the injured.

They cut off their clothes, wrapped them in foil blankets and tried to keep them calm by telling them everything will be alright.

At some point, someone made the decision to head back to the mainland with the 23 burnt people who'd been rescued from the island. They all needed treatment.

Five of them were critical.

Hopkins spent a lot of his time with a young tourist couple who were drifting in and out of consciousness. He tried to get as much information about them as he could so he could tell paramedics.

"My fear now is that they didn't make it. There were five critical people on our boat and there's been five fatalities confirmed … they were just so badly burnt."

Halfway back to the mainland, a coast guard boat dropped off some paramedics who tried to give people pain relief.

But they struggled to find veins under their burned skin as they bounced over the waves.

"I have no idea how long it took to get back, we just motored as fast as we could. But at this stage people started to go into shock.

"And they're cold because they're wet from pouring water on their burns.

"So instead of asking for water, we were asking for coats and jackets. People were taking their T-shirts off to give us clothes to try and keep people warm on the way back.

"I remember three Asian tourists that huddled together under a big waterproof duffle bag."

An aerial view of White Island after the volcanic eruption. Photo / George Novak

When they got back to shore, the paramedics took over while a bus took the uninjured back to the White Island Tours offices were they were met by officials.

They were helped with getting in touch with loved ones.

Hopkins managed to call his wife, who was at home, and let her know he and Lilliani were safe and when they were cleared, went back to Hamilton.

"The hard thing is I know that we've lost people, so you start analysing. Was there something I could have done different?

"Was there something I could have done to save someone?"