Mt Tongariro has erupted with a 2km-high ash plume seen in the sky and residents reporting the sulphur is making it harder to breathe.
GNS Science confirmed the eruption, at the Te Maari crater, happened shortly after 1.20pm. It lasted for about five minutes. It has updated the alert on Tongariro to 2, meaning there is "minor eruptive activity". The aviation colour code has been lifted to red, meaning there is "significant emission of ash'' into the atmosphere.
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Wellington Airport spokesman Greg Thomas said no flights had been affected yet, however that could change and the situation was being monitored.
Up to 90 Napier schoolchildren, two hours into a tramp on the Tongariro track, are safe and well.
Two bus drivers from Nimon and Sons, who took the children up to the mountain, had reported back to their base that they could see a plume 2km high, a spokesman said.
Conservation Department (DOC) area manager Jonathan Maxwell said 30 to 50 people were being evacuated from the Tongariro Crossing track. No injuries had been reported. State highways in the area had been closed.
A national advisory has been issued by Civil Defence saying regions from Waikato down to Hawke's Bay could be affected by ash cloud.
"Minor volcanic activity is occurring at Tongariro - Te Maari craters and could be hazardous in the immediate vicinity of the craters.
"Light volcanic ash fall can be anticipated downwind of Tongariro and may impact the following areas or regions: Waikato; Hawkes Bay; Gisborne and Bay of Plenty.
Genesis Energy was shutting production at its Tongariro hydro scheme site south of Lake Taupo.
Civil Defence was warning people to stay indoors if ash was present.
"Light volcanic ash fall can be anticipated downwind of Tongariro and may impact the following areas or regions: Waikato; Hawke's Bay; Gisborne and Bay of Plenty.
"Volcanic ash could be a health hazard, especially if you suffer from breathing difficulty. If outside, seek shelter (e.g. in a car or building)."
It was advising people to close all windows and cover their mouths if caught in the ash. People should stay out of designated restricted zones.
DOC had a helicopter in the air and was canvassing the volcano to see if they could locate anyone on the mountain, a Taupo Council spokeswoman said.
"There is a helicopter looking to see if there's anyone around, any visitors on the mountain to make sure everybody is safe," she said.
Taupo Council's civil defence emergency manager Phil Parker, who coordinated the response last time the volcano erupted, was working with DOC and other organisations.
It was unclear at this stage who would be coordinating the response today, but the appropriate authorities were communicating with each other, the spokeswoman said.
"We're just watching it, trying to get a better assessment," she said.
Massey University is flying two vulcanologists up to study the eruption and already has five students and staff on the ground near the mountain.
More scientists are also on stand-by depending on the size of the eruption.
Massey University vulcanologist Professor Shane Cronin said they will monitor the ash levels and take samples to determine the likelihood of another eruption.
He said the initial suggestion was that the eruption was roughly the same size as the previous Tongariro eruption in August.
Police are assisting the Department of Conservation following the eruption.
Taupo police area commander Inspector Steve Bullock said there were no road closures in place "but I would discourage sight-seers from travelling to the area. We don't want unnecessary congestion to contend with, and want to ensure the road network remains free-flowing just in case there is any further volcanic activity."
There have been no immediate reports of any injuries.
Lake Rotoaira resident Robyn Bennett said there was a big, black ash cloud over her house, which was about a kilometre from the eruption site.
"It's just blew her stack," she said.
She said the air smelled of sulphur.
"It's hard to breathe if you go outside, it's pushing out quite heavily." Bennett said she didn't hear the eruption but it looked like a new vent had formed in front of a previous eruption crater. The ash cloud was moving east towards Napier and Taupo.
Ann Lambert, owner of the Rainbow Motel at Tokaanu, near Turangi, said she had not been aware of any noise, unlike the previous time Tongariro erupted when there had been a "huge loud noise".
"We weren't aware it had happened. We just looked up and saw it," she said.
"It's just a grey cloud at the moment ... It's not as imposing as the last time."
Kathleen Konui, who lives at Otukou Marae "just below" the mountain, said she had heard a sound like a shotgun going off.
"The mountain was all covered with white smoke," she said.
In the hour or so since then the air had cleared, although she could still see some smoke coming from about four holes on the mountain.
"I'm standing here now looking at them."
The sky was too hazy for her to be able to see a plume from the eruption.
At 1.30am this morning a New Zealand Couriers truck driver reported a strong smell of sulphur on the Desert Road while Motuoapoa resident Cindy Greaney said she noticed an "obvious smell of sulphur" at 6am.
This is the second eruption this year. The Te Maari crater erupted on August 6, the first time in more than 100 years.
The eruption, on August 6, widened and deepened the crater and reactivated vents which had been covered up in the 116 years since it last erupted in 1896.
Ruapehu has also been active recently but has not erupted. Pressure was building under the volcano and there was an increased likelihood of an eruption, GNS said last week.
The volcanoes are close to each other but scientists did not believe that the activity at both volcanoes was related.
However, they couldn't exclude the possibility, GNS vulcanologist Nico Fournier said earlier this week.
"We don't have evidence at the moment that the activity of the two volcanoes are related," Fournier said. "But we can't exclude it entirely."
GNS vulcanologists were researching if activity at the two volcanoes was connected and also were looking at the relationship between earthquakes and volcanic activity.
A series of earthquakes rattled the ground beneath Tongariro in the weeks leading up to the August eruption and another series of quakes have shaken the ground beneath Ruapehu in the last few weeks.
- Reporting by Fairfax NZ and Chris Hyde
- Manawatu Standard
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