Mt Tongariro has erupted this afternoon, spewing ash and gases into the air, causing flight cancellations and closing the Tongariro crossing track.
The mountain, which erupted for the first time in more than a century in August, erupted again at 1:20pm, GeoNet has confirmed.
The cloud came from the Te Maari Crater, seen to the northwest of the mountain, in a similar location to the August 7 eruption.
The Department of Conservation says the Tongariro Crossing track has been closed and the 50 people using the track at the time of the eruption are on their way out of the area.
One of the groups on the track was a group of school children from Whangaparoa who are expected out at 4:30.
Another group of 300 students from St Kentigern College were set to start the track but have been held back.
Peter Gent, who was walking the Crossing at the time, says a significant plume came out of the mountain.
“It’s not one of the major volcanoes. But the plume is really high, about 6,000 metres and it looks like it could affect aircraft movements at that height," he said.
“My car is parked in the path of the plume so it might get some ash,” he says.
Staff at the nearby Tongariro Outdoor Pursuits Centre say they are not too worried and the eruption has finished.
However, Tongariro National Park area manager Jono Maxwell says there is concern for trampers on the mountain.
“There has been increased activity there this afternoon; we’re naturally concerned for the safety of the people on the alpine crossing and in the immediate vicinity.”
Eye witness Christian says his office looks directly at the mountain.
“We just saw this big white plume of smoke coming out of the mountain – it looked a little bit like a mushroom cloud. At the moment we can see its actually filtering out a little bit.”
“I’m around 1800 metres high and the plume has gone up really high, way above me," says Mr Gent.
"The weather is pretty clear and you can see it coming out the mountain."
GNS Science has upgraded its aviation code to 'red', meaning significant emission of ash into the air is likely.
The Civil Aviation Authority’s Peter Lechner says there is no advisory for airlines but he will continue to monitor the situation this afternoon.
“At this stage the airspace over the mountain is not restricted but we are ensuring airlines know about it,” he says.
Air New Zealand have cancelled four services from Whakatane, Tauranga, Rotorua, Taupo. No other flights are affected at this stage.
There is no smell at this stage, just lots of ash and steam. Mr Gent says the plume is fairly static.
The August eruption surprised geologists. There were no injuries or serious damage, but ash blanketed the Tongariro crossing and neighbouring farmland.
GNS Science had just last week issued a warning about neighbouring volcano Mount Ruapehu.
It had raised its aviation alert level from green to yellow after measuring dramatic temperature changes beneath the Crater Lake, prompting the Department of Conservation (DOC) to tell people to stay away from Ruapehu’s upper slopes.
Last week, DOC had said it was confident people could freely enjoy Mount Tongariro.
“People should not feel that they should change their behaviour or planned activities for Tongariro,” DOC analyst Harry Keys said at the time.