White ash covered the area around Te Maari crater on the northern slopes of Mt Tongariro as the volcano continued to vent steam yesterday afternoon, after it blew ash into the air about 1.30pm.
Local Constable Aaron Owen said he was awestruck seeing the crater blow as he travelled through the Tongariro National Park. He did not hear anything as the crater blew but watched the spectacle for a couple of minutes.
A tour operator from Walking Legends on Lake Waikaremoana told the Chronicle he was heading to Ketetahi, close to the crater, to pick up six Australian tourists who were walking the Tongariro Alpine Crossing. Department of Conservation Whakapapa area asset manager Neil Ranford said the eruption was "just a burp". He waited at the roadblock on the intersection of State Highway 47 and Mangatepopo Rd for tourists who had driven up the road, to come off the mountain. Mr Ranford said he understood there were about 200 people on the crossing.
"A helicopter saw a group of people running down the track just after the eruption," he said, but he did not think anyone was in danger.
Further along the highway at the SH47/SH46 junction, Downer worker Tirra George from Turangi had set up a roadblock at 2pm. Only locals and tour operators were allowed to go down SH46.
Mr George said he had driven along SH46 and there was no ash "like last time".
Ash and gas blasted 2km into the sky, authorities said, prompting police and DoC staff to close the Tongariro Alpine Crossing at Ketetahi and Mangatepopo roads, where the track starts and finishes.
All those on the crossing were thought to be safe and were making their way off the track, DoC community relations manager Kim Alexander-Turia said.
"The difference between this eruption and the last eruption is there's no volcanic rocks coming out, so we're just letting people quickly and safely come off in their own time, calmly."
The eruption prompted an aviation alert increase to orange.
Sara Page from GeoNet said the alert was upgraded because the eruption was under way with "significant ash in the atmosphere".
Air New Zealand said there may be delays or cancellations on domestic services to airports east of the mountain.
But the airline said it would adjust flight routes and altitudes if required, ensuring aircraft remained clear of any ash.
GNS Science duty volcanologist Nico Fournier said there was one eruption - "essentially one explosion, and it was not sustained".
Dr Fournier said the eruption was not very loud and was smaller than an earlier eruption in August.
Last week, GNS Science increased the likelihood of neighbouring volcano Mt Ruapehu erupting, following increased activity on the mountain.
Dr Fournier said there was "quite a bit of gas" but it was quietening down.
Staff and students from Tamatea Intermediate in Hawke's Bay are safe and well after being on the Tongariro Track at the base of the volcano during the eruption.
About 100 staff and students were about two hours into the track when the eruption occurred.
A school spokesman said the staff and students were okay and were coming down the mountain.
The Ministry of Civil Defence and Emergency Management issued a national advisory just under an hour after the eruption.
It said "minor volcanic activity" at Tongariro's Te Maari crater could be hazardous in the immediate vicinity.
Light volcanic ashfall was anticipated downwind of Tongariro and could fall in Waikato, Hawke's Bay, Gisborne and Bay of Plenty.
People living in or near the affected areas were advised to stay indoors and close windows and doors if ash fell. People who were outdoors should seek shelter.
Civil Defence said ash could be a health hazard, especially for people suffering breathing difficulties.
People affected by ashfall should wear a dust mask over their nose and mouth and protect their eyes.
Robyn Bennett, who lives 6km from the mountain, said she could see the plume of ash rising into the sky and sulphur-smelling ash had been raining down on her home.
"It's sitting under some cloud and that's why it's pushing down on to us," she said. "It smells worse than rotten eggs."
Ms Bennett did not think she and her husband would need to leave their home, "not unless she starts spewing out a whole lot of red rocks", but they were waiting to hear from Civil Defence or DoC.
James Perry, who works at the Lake Taupo Hole in One attraction on the resort town's lakefront, had a clear view of the mountains of the central plateau and saw the ash as soon as the eruption occurred.
"It basically went straight up and did the mushroom cloud, and then the wind's just spread it from there," he said.
Tongariro, in the centre of the North Island, erupted in August for the first time in 115 years, sending ash as far east as Napier.
According to GeoNet, Tongariro is a complex of multiple volcanic cones constructed over a period of 275,000 years.