At least one person is dead, and up to 27 people are still missing, after White Island erupted, spewing plumes of smoke into the air on Monday.
Up to 100 people were initially believed to be on or near the island at the time of the eruption around 2.30pm, but police now believe there were fewer than 50.
Prime Minister Jacinda Ardern said during a press conference that she would be heading to the scene of the eruption on Monday night.
She said those missing and injured were both New Zealand and foreign tourists. The Ministry of Foreign Affairs have set up their systems to respond to concern from those abroad.
"An active police search and rescue operation is underway," she said.
Police national operations commander, Deputy Commissioner John Tims, said there had been one confirmed fatality, but there would likely be more.
"At this stage, it is too dangerous for police and emergency services to go on the island," he said.
"We will provide more details as they come to hand."
Tims said 23 people had been transported back from the island, but it remained unclear how many were still missing- but it could be around 27.
The person who died had been transported from the island.
Meanwhile, Deputy Prime Minister Winston Peters has Tweeted his condolences.
"Deep sympathy to all those grieving due to the news coming from White Island," he said on Twitter.
Patients arrive
People covered in ash could be seen arriving for treatment after being transported from rescue helicopters.
She was was not able to confirm whether or how many passengers were injured.
It is understood passengers from the Ovation of the Seas cruise ship, currently visiting Tauranga, were among those visiting White Island at the time of the eruption.
A spokesperson for Royal Carribean Cruises, Annie Standen, would not confirm if passengers were involved but said a representative from Ovation of the Seas was at the cordon.
She was was not able to confirm whether or how many passengers were injured.
"At this stage we are still gathering information."
Don Richards, owner of the River to Sea BnB, said he was located within the cordon on Muriwai Drive and could see steam coming off the island and fleets of ambulances assembling at the wharf and helicopters landing.
He saw two White Island Tour boats coming in from the island, the second boat came in at speed about 4pm and "was covered in ash".
Some of the passengers off the boats appeared to be walking, some were sat wrapped in emergency blankets, while others were being carried in on stretchers.
Meanwhile, Prime Minister Jacinda Ardern was late to her regular Monday post cabinet press conference as she was seeking advice on what was happening at White Island.
"Police search and rescue are supporting the emergency management crews," she said.
"This is evolving at this stage ... obviously it does appear to be a very significant issue."
St John confirmed that they are working with the Coastguard and the local DHB and had sent one ambulance crew to the island.
There are five helicopters that have been dispatched - onboard one helicopter is St John Clinical Director Dr Tony Smith who will set up a triage on the Island.
An image captured at 2.10pm from a GNS camera showed people were on the island at the time of the eruption.
GNS duty Vulcanologist Geoff Kilgour expressed concern for their safety.
"Our monitoring data shows that there was a short-lived eruption that generated an ash plume to 12,000ft above the vent," he said in a statement.
"Ash has covered the main crater floor as seen in our webcam images. Ash fall appears to be confined to the island and we do not expect more than a minor amount of ash to reach East Cape in the coming hours."
GNS monitoring equipment was still operating, and there had been a steady decline in activity since the eruption.
"There remains significant uncertainty as to future changes but currently, there are no signs of escalation."
A spokesman from National Civil Defence said they were still trying to pool all of the information about the eruption.
"All we know is that there was a burst at around 2.15pm. There's reports [of people] on the Island and police are leading that response, there's been a volcanic alert at level 4 which means its a moderate eruption with hazards on or near the volcano."
Volcanic Air confirmed it had a helicopter on White Island at the time of the eruption.
Five people had flown to the island in the helicopter, but all are accounted for and have arrived back in Whakatāne by boat.
The company had enacted its emergency response plan and said its priority was looking after the pilot and passengers.
They said it was inappropriate to comment further and would offer any assistance it could with the rescue operation.
The company has been taking tours to White Island since 1992 and works closely with GNS Science to minimise any risk.
Eruption not unexpected
GeoNet Vulcanologist Brad Scott said it was always a surprise when a volcano erupted, but it wasn't completely unexpected.
"But as you are well aware, volcanic unrest has been occurring at White Island for several weeks now, so it's not a total surprise that this has led to a total eruption and we have alluded to this possibility for some time," he said.
In October Stuff reported that Sulpur dioxide gas output and volcanic tremor levels at Whakaari/White Island are at the highest levels since 2016, possibly suggesting the volcano was entering a period where an eruption was more likely.
SO2 gas at volcanoes originates from magma (molten rocks), and is measured by scientists as a way to try to get an indication of what is happening to a volcano's magma system.
My husband is out at sea and it looks like White Island May have erupted
He said any adverse health effects for those on the mainland were very unlikely. "On the island however, unfortunately, there will be injuries - rocks and material thrown out from the volcano would have the possibility to kill or injure anybody nearby. "It was a significant eruption and we are concerned for anybody who was on the island at the time." Scott said the last time White Island erupted was in 2016, this was described as a 'minor' eruption. "As White Island is an active volcano, it can erupt and this cannot always be predicted."
Huge plumes of smoke
Meanwhile a large plume of white smoke was visible from the mainland during the eruption. Several people messaged Bay of Plenty news service SunLive saying the eruption had happened.
"My husband is out at sea and it looks like White Island May have erupted," one reader told SunLive.
"It went from nothing to that suddenly popping up and expanding."
Another reader said "massive amounts of smoke just came out of White Island."
"And it is growing."
Opotiki resident Maree Reeve said "I certainly haven't seen a puff like this, possibly in the whole 18 years of living here".
"You can see stuff (ash maybe) falling from the cloud."
Meanwhile, emergency services have cordoned off Muriwai Drive to the Whakatane Heads in the wake of the eruption.
Lawyer's office, Buddle Bentley McLeary, confirmed the road has been cordoned off.
"One of the ladies had just left our work and said the emergency services are all there and the road is blocked off. So we can get out but no one can come down," they said.
She could see plumes of smoke.
"It's quite scary, it doesn't happen this big, apparently it's up to a level four which is quite high."
"It has been happening for a while, but not this extreme, so who knows what will happen but just have to keep up to date with everything and be cautious."
She said they saw tours boats going out to the island all the time
Ash disruption
A METservice spokesman said the volcanic ash advisory service were not available to comment at the moment as the team were busy liaising with aviation authorities in the area.
The spokesman said at this stage METservice were continuing to monitor the situation.
Airlines in New Zealand said there has been no effect to flights at this stage, with JetStar also confirming that there had been no impact to operations.
However, they were monitoring the situation closely.
Air New Zealand said the eruption has not affected them and directed further queries to Airways.
Airways has been contacted for comment.
Most active volcano's history
White Island, 48km offshore from Bay of Plenty, is New Zealand's most active cone volcano, built up by continuous volcanic activity during the past 150,000 years.
With 70 per cent of the volcano under the sea, it is also the country's largest volcanic structure.
GeoNet said the longest historic eruption episode was from 1975-2000. During that time, many collapse and explosion craters developed.
For long periods active vents in the craters emitted volcanic ash.
Men once lived and worked on the island.
From the 1880s, they mined the sulphur, for many uses from gunpowder to fertiliser.
On September 21, 1914, a sudden lahar in the middle of the night swept away the mine buildings in the crater and the 11 men asleep in their beds.
The only survivor was a tabby cat, Peter, who was rescued a week later when the disaster was discovered.
