In the aftermath of the deadly eruption on New Zealand's White Island, questions are being raised about why tourists were allowed on an active volcano.
Five people are dead and eight people - including New Zealanders and tourists from Australia, Britain, the US, China and Malaysia - are unaccounted for and presumed dead, Prime Minister Jacinda Ardern said on Tuesday morning.
Later in the day she told Radio New Zealand that "there will be questions that are being asked, that will need to be answered ... by the appropriate authorities."
"It's an unpredictable live volcano," Ardern said.
While national geological hazard monitoring system Geonet tracks the the volcano's activity, the island is privately owned and it is up to tour operators to decide when to visit.
Geonet had put the volcano on level two, indicating minor volcanic unrest. It was on level one 1 ahead of its previous eruption in 2016.
White Island sits on the Pacific Ring of Fire, an area known for frequent earthquakes and volcanic eruptions, and is the emergent peak of a large submarine volcano that lays 48 kilometres offshore from Whakatane on the east coast of New Zealand's North Island.
One of the tour operators, White Island Tours, said on its website - which has been taken down - that it operated during varying alert levels, but added that "passengers should be aware that there is always a risk of eruptive activity regardless of the alert level".
The website also stated that the tour company "follows a comprehensive safety plan which determines our activities on the island at the various levels."
Paul Quinn, chair of Ngati Awa Holdings which owns White Island Tours, told Radio New Zealand the heightened alert levels on the volcano over the last few weeks didn't meet its threshold for stopping operations.
"Level 3 and above we liaise more directly with GeoNet but level 2 is still within our operational guidelines," he said.
Tourists are only allowed to land on White Island as part of a tour group and are provided with hard hats and gas masks to protect against the sulphurous steam. Around 10,000 tourists annually visit White Island.
Ross Dowling, tourism researcher at Edith Cowan University in Perth, said that "the number of tourists visiting active volcanoes is increasing globally as part of an increase in both geological tourism and adventure tourism.
"Part of the attraction is to visit an unpredictable natural environment and for most tourists they assume that they will be able to visit such dangerous sites in relative safety."
"White Island has been a disaster waiting to happen for many years," Ray Cas, emeritus professor at the School of Earth, Atmosphere and Environment at Monash University, told the Science Media Centre.
"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," he added.
Vulcanologist Shane Cronin told Science Media Centre that "sudden, unheralded eruptions from volcanoes such as White Island can be expected at any time."
Magma was close to the surface, and the heat and gases formed hydrothermal systems.
"We know hydrothermal and so-called 'phreatic' eruptions can occur suddenly and with little or no warning because they are driven by the expansion of super-heated water into steam," he said.
Australian Associated Press