A professor of Geosciences at Monash University says White Island has been a disaster waiting to happen for many years and it's always been too dangerous for daily tour groups to visit.
Emeritus Professor Ray Cas from the School of Earth, Atmosphere and Environment, Monash University is internationally known in the field of physical volcanology, including the hazards posed by volcanic eruptions.
"Having visited it twice, I have always felt that it was too dangerous to allow the daily tour groups that visit the uninhabited island volcano by boat and helicopter," Prof Cas said in comments published by the Australian Science Media Centre.
He said the island "has been a disaster waiting to happen for many years".
David Rothery, Professor of Planetary Geosciences at Britain's Open University, told SMC Whakaari had five separate eruptive events since 2000 and yesterday's was the sixth and biggest.
"Background activity on White Island had been increasing over recent days, as reported by GeoNet," he said.
"I understand that White Island is privately owned, and that the state has no control over access.
"In view of this unforecast (and possibly unforecastable), sudden moderately large and fatal eruption, questions will be raised about the duty of White Island Tours in allowing their clients to go ashore - but thousands have done so previously to experience the sights and sounds of an active (but not usually erupting) volcano.
"I was in New Zealand three years ago, and had an earthquake not prevented my travelling from the South Island I would probably have visited White Island myself.
In global terms, it was not a major eruption and was extremely unlikely to mean increased volcanic activity elsewhere, he added.
Lecturer in Geophysics at the University of East Anglia in England, Dr Jessica Johnson, said the eruption was not completely unexpected.
"Levels of activity at White Island/Whakaari have been relatively high since September, and even more elevated over the last couple of weeks, with increased numbers of small earthquakes and more volcanic gas detected than usual," she said.
"White Island / Whakaari is a very beautiful and interesting destination that naturally attracts tourism. It is very difficult to say whether tourism should be allowed there.
"The volcano has displayed similar unrest in the past with no major eruptions. The most that the scientists can do is continue to monitor the volcano and issue information when it is available."
Paul Quinn, chair of Ngāti Awa Holdings, which owns White Island Tours, said the heightened alert levels on the volcano over the last few weeks didn't meet its threshold for stopping operations.
He said White Island Tours had previously taken visitors to Whakaari / White Island when the volcano had been at a level 2.
He said that alert level was within its operating guidelines.
"GNS do the monitoring, and they advise us if there are any changes, and we operate around their guidelines in terms of what levels are stipulated.
"Level 3 and above we liaise more directly with GNS but that level 2 is still within our operational guidelines."
He said ceasing tours had not been discussed, and everyone was comfortable to continue operating.
Mr Quinn would not say whether changes need to be made.
"It's too early to worry about those things."
The daily tours bring more than 10,000 visitors to the volcano every year.
White Island is New Zealand's most-active cone volcano, built up by continuous volcanic activity over the past 150,000 years, according to New Zealand science agency GeoNet.
About 70 percent is under the sea, making the massive volcanic structure the largest in New Zealand.
The volcano's last fatal eruption was in 1914, when it killed 12 sulphur miners. There was a short-lived eruption in April 2016.
GeoNet raised the alert level for the White Island volcano last month because of an increase in volcanic activity.
GNS volcanologist Michael Rosenburg said at the time there had been an increase of sulphur gas from deep inside the volcano and an increase in tremors.
He said the changes may or may not be a signal that something is happening.
"White Island volcano is really complicated and just because one thing changes, it doesn't necessarily mean that everything else will change and it doesn't necessarily mean that this is going to lead to an eruption," he said in November.
Dr Rosenburg said tour groups could still visit the island.
GNS Science, in June, said the volcano has historically high levels of sulphur dioxide - the second highest since regular measurements began in 2003.
Duty volcanologist Agnes Mazot said there had been clusters of earthquakes nearby recently, but the relationship between them and the high gas readings was unclear.
She said the change in gas readings was significant, and there was potential for an eruption.
The volanic alert level was also raised in June this year after moderate unrest.
And in May this year, there was a swarm of almost 200 earthquakes rocking the island. GNS duty volcanologist Natalia Deligne said it was not unusual to have so many earthquakes in the area.
GNS said earthquake sequences are relatively frequent near White Island.
White Island also had its alert raised in September 2016 after a small eruption. The volanic alert was raised to level 3 after showing heightened unrest.
A witness who was on the island at the time reported seeing black smoke.
Earlier in 2016, a new crater was formed following a small eruption. GNS said the discovery of a new crater and gas output was found after an aerial inspection.
In October 2013, the Bay of Plenty volcano erupted throwing mud and steam into the air.
It also erupted in August 2013 blowing steam and a small amount of ash four kilometres into the air. Vulcanologist Nico Fournier told Morning Report at the time that recordings indicated the volcano is not presently building up to a big eruption.
He said the island is privately owned so people cannot be stopped from visiting, but they should exercise their judgment.
In January that year, Bay of Plenty Regional Council warned that seismic activity on the island posed a greater than usual risk to visitors.
At the time, the crater lake was drying out and in the last and mud and rocks had been hurled into the surrounding area.
Volcanologist Gill Jolly said in January 2013 the activity on the Bay of Plenty island was some of the most vigourous for many years and explosive eruptions could occur at any time with little or no warning.
Ms Jolly said a high level of caution should be taken if visiting the island.
GNS volcanologist Brad Scott visited the island on 22 January, 2013 and said the hydrothermal activity is some of the most active he has seen there for many years.
Mr Scott said the level of hydrothermal activity usually leads to stronger volcanic activity and there was a 50-50 chance of an eruption.
However, he said it was not clear which way the volcano is going to go, and people visiting the island should be aware of the risk.
The volcano erupted in early August, 2012, displaying the most volanic activity since 2001.
Scientists, at the time, warned visitors White Island to stay alert, saying the risk was still higher than normal.