Two more people have died following the volcano eruption in New Zealand, raising the number of people killed to eight.

Both people were being treated in hospital for their injuries when they died, police have said.

Nine others are still missing after the eruption on White Island, off New Zealand's North Island on Monday, but ever-increasing volcanic activity is preventing the authorities from returning.

Emergency services have said the island is too dangerous, with "serious physical and chemical hazards" standing in the way of any potential search operation.

Seven Australian nationals are unaccounted for, along with two New Zealanders.

The nationalities of the latest two victims have not been given, but they were among 30 people previously said to have been in hospital after suffering burns following the incident on Monday.

Of those being treated, all but five were in a stable but serious condition.

Due to the unprecedented numbers of burn victims at one time and the nature of their injuries from toxic volcanic gases, more than one million square centimetres of skin has been ordered from America to treat patients.

In this satellite image taken and released on May 12th 2019 by Maxar Technologies, steam rises from the volcano on White Island off the coast of Whakatane, New Zealand | Image: AP/Press Association Images

Dr Peter Watson, clinical director at Middlemore Hospital, said some patients have burns on up to 95% of their bodies, while the average is 40-50%, and 22 remain on airway support due to burns affecting their lungs.

There were 47 people on the island at the time of the eruption; 24 from Australia, nine from the US and others from countries including Germany, Britain, China and Malaysia, plus five from New Zealand.

Many had taken a day trip from the Royal Caribbean cruise ship Ovation of the Seas.

Tour guide Hayden Marshal-Inman, from New Zealand, was the first person to have died to be publicly named.

On Wednesday afternoon, Australians Julie Richards, (47) and her daughter Jessica (20) from Queensland were also confirmed to have died.

Police have also identified the remains of Gavin Dallow, while his stepdaughter Zoe Hosking is among the eight people officially named as missing.

The others unaccounted for include Jessica Richards (Australia); Krystal Browitt (Australia); Richard Elzer (Australia); Karla Matthews (Australia); Julie Richards (Australia) Tipene Maangi (New Zealand) and Hayden Inman (New Zealand).

On Tuesday, New Zealand Prime Minister Jacinda Ardern told the parliament the "scale of this tragedy is devastating".