© Greg Bowker
An aerial view over the Tongariro National Park.
A "sudden rise" in volcanic activity at Mt Tongariro has prompted scientists to lift its volcanic alert status for the first time.
But local businesses and conservation authorities remain unconcerned as they seek to reassure visitors it is "business as usual" at National Park.
GNS Science this afternoon lifted Mt Tongariro's volcanic alert status from level zero to level one, and increased the aviation status from green to yellow.
It said a series of more than 20 "small" volcanic earthquakes had been recorded at Tongariro since July 13 - more than the average of two per year according to historic seismic data.
The quakes, below a magnitude of 2.5 and between 2-7km deep, were recorded in a cluster zone between Emerald Crater and Te Maari craters.
The sequence of earthquakes soon declined but restarted on Wednesday and increased in number yesterday and today.
GNS volcanologist Brad Scott said it was the first time the alert level had been lifted at Tongariro since the alert system was introduced.
"It's displaying some form of unrest. We don't know exactly what's driving it, if we did we'd be saying."
To get a clearer picture, GNS would deploy portable seismic recorders around the epicentres of the earthquakes and conduct sampling of selected hot springs, crater lakes and fumaroles in the area.
"We've got our permanent networks out giving us data in real time... (and) we want to compliment that with some more data, just to add to our knowledge."
Mt Tongariro is a volcanic complex that lies to the north of Ngauruhoe and consists of numerous craters and vents.
There are six alert levels of volcanic action, increasing in seriousness from zero to five. Alert level one indicates "signs of volcano unrest".
For the alert level to be lifted to two - "minor eruptive activity" - there would need to be an eruption and there was no indication that would happen.
The aviation status yellow also acts as a warning of increased unrest.
Department of Conservation local conservation analyst Harry Keys said GNS Science was dealing with the matter and the department did not need to take any action at this stage.
The popular Tongariro Alpine Crossing passed close to Te Maari craters, where the most recent ash eruptions took place from 1855 to 1897.
But there was no hazard at the moment and the crossing would remain open to the public.
"There are public safety matters if the volcano starts getting active, but at the moment the volcano is not getting active and it may not ever get active," he said.
"We've got everything ready if we have to do anything. We will then go to the next stage, but at the moment we're not doing anything."
Dr Keys said he would not expect more or fewer visitors at the moment.
"It's definitely business as usual. People might make their own decisions, but there's no reason at the moment they should make any decisions about what they've planned."
National Park Business Association chairman Murray Wilson said the only problem with volcanic activity was when it interrupted visitor flows.
He had been at a regional tourism meeting today but the issue was not even raised.
"It's just a fact of life around here and I don't think anyone around the place will be to excited about that - it's probably more of a technical response than a physical response."
Mr Wilson said "media hype" had been the biggest issue the last time neighbouring Ruapehu had erupted in the 1990s.
"The people around here depend on uninterrupted visitor flows. Last year we had interrupted visitor flows because of the Rugby World Cup - as soon as the rugby started, people tended to stay at home and go to the rugby matches."
He did not think there would be much impact unless it was "over-reported and people get worried".