Thick clouds of sulphurous ash and a stained sea: Whakaari / White Island after the eruption

A doctor who landed on Whakaari / White Island in the aftermath of Monday's eruption says there was a strong smell of sulphur in the air.

St John medical director Dr Tony Smith was one of the doctors onboard an Auckland-based Westpac rescue helicopter, when they were dispatched to Whakatāne.

After fuelling up at Whakatāne Airport, they headed to the island.

"We arrived to a large plume of smoke and a thick cloud of sulphurous ash, almost forming like a fog," he said.

"There was a thick yellow stain running out to sea and it was clear from the extensive staining of sulphurous ash that there'd been a significant explosion."

There was a window of opportunity to safely land on the island, just on the beach near where the boats that visit the island offload their passengers, Dr Smith said.

He and three intensive care paramedics spent about half an hour on the ground, with the helicopter remaining immediately overhead, in case they needed to leave quickly.

"We were able to establish that unfortunately nobody remained alive and at that point we left and returned to the mainland, because we knew that there were large numbers of very badly injured patients."

On the island, Dr Smith said there was an incredibly strong smell of sulphur, even through the respirator masks they were wearing.

"Any exposed area of skin, for example our necks, our faces and our eyes were stinging pretty severely from contact with the sulphur.

"We're certainly not left with burns, but we left with very sensitive skin, very sensitive eyes and very sore throats as a result of being in contact with the sulphur."

Back in Whakatāne, the next task was to get the injured who had arrived at the airport or at the harbour to hospital.

A number of helicopters and small planes, from as far south as Christchurch and as far north as Whangārei, were brought in to take people with serious burn injuries to hospitals around the country with specialist units.

The injured were taken to Auckland City, Middlemore, Waikato, Tauranga, Hutt Valley and Christchurch hospitals.

Dr Smith said the scale of the injuries was like nothing he had seen before.

"This is certainly the first time in my experience, and I've been with St John now for over 20 years, that we've had to deal with something like this.

"Most of the patients had burns, some of them had limb fractures, presumably from either being thrown against an object or having an object like a rock thrown against them.

"But most of the patients had burns and the burns ranged from moderate burns right up to very severe and life threatening burns as a result of a combination of hot ash and hot liquid."

Dr Smith said even a moderate burn would involve hours and hours of reconstructive and lifesaving surgery and days of intensive care.

"The ongoing treatment for these patients in hospital is very intensive and for any hospital to have to deal with more than three or four of those patients at any one time is a really big ask and we've got a number of hospitals that are dealing with or three times that number of patients with severe burns and so this is a really big incident for the healthcare system in New Zealand."

Associate Professor David McBride is from the Dunedin School of Medicine and specialises in military medicine with expertise in toxic substances.

He told Morning Report that because helicopter crews who landed on the island reported difficulty breathing, even through their masks, it suggested the presence of sulphur dioxide and hydrogen sulphide, following the eruption.

He said hydrogen sulphide is particularly injurious and occurs in geothermal areas and also in sewage works. Mr McBride said there have been three deaths in Rotorua due to hydrogen sulphide where people were incapacitated by it and died shortly afterwards.

He said survivors would also be suffering from smoke inhalation, as well as gas damage to the lungs. He said some people who have suffered gas inhalation may heal, but some continue to have an asthma-type condition as a result of the exposure.

Mr McBride said it's likely to take those who were on White Island longer than usual to recover from any lung issues.

"Smoke inhalation is difficult to deal with, sulphur dioxide and hydrogen sulphide, if you survive the initial assault, their active airways component usually clears up in a week or two, but these are more complex injuries and I'm not an expert but I would say it would take them longer to recover."