A truck driver, who was heading across Desert Road when Mount Tongariro erupted, said the noise was like a train.
The eruption happened at around 11.50pm at the Te Maari craters near the Ketetahi hot springs, on the northern side of the mountain, GNS Science says.
Witnesses reported seeing "flame-like explosions", red hot rocks being thrown into the air, lightning, hearing loud explosions and one witness reported a cloud of ash coming from "a new hole in the side of the mountain".
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"There was a big flash," truck driver Tama Coker said.
"I thought it was lightning and then it started raining sand. It was pretty thick. I heard it rumbling like a train."
Coker said when he drove through the Desert Rd he could not see the white lines on the road.
"I could just see the yellow glare on the mountain. I only had visibility of about 10 to 15 feet in front of me. It was a bit scary.
"It's something I'll probably never see again in my lifetime."
He said the sand-like ash had covered his truck, and the sign writing on the trailer was barely visible.
Local resident David Bennett who lives on the southern shores of Lake Rotoaira, about 6km away from the eruption, said he heard and saw the mountain erupt just before midnight last night.
He considered himself fortunate no rocks landed on his house last night.
"There were rocks being thrown out. It was like thunder and lightning and fireworks," Bennett said.
There was a lot of ash on State Highway 46 this morning - the roadway linking the Desert Road with the Whakapapa Ski Field.
"It was spectacular. There were rumbling sounds and thunder and lightning coming out from the base of the eruption," Bennett said.
There were no cars in the Tongariro Crossing Carpark when he visited the area this morning, Bennett said.
He said there were about 12 houses on the Southern shores of Lake Rotoaira and when the mountain erupted locals made sure all the residents living in the area were safe.
His house is situated about five kilometres away from the roadway leading to the northern end of the Tongariro Crossing.
A few locals did drive to the Hirangi Marae in Turangi but most just stood and watched the spectacular show.
"It's a volcano. If it goes, it will go. We'll all be vapourised. Ruapehu and Ngauruhoe have erupted regularly over the years. Now it is Tongariro's turn."
Bennett understood nobody overnighted at the Ketetahi Hut at the northern end of the Tongariro Crossing last night and that the Ketetahi Springs area had not been affected by the eruption.
He also understood a new vent had opened up near the Te Maari Crater area on Mount Tongariro.
A receptionist at the Chateau Tongariro, Maria Dadal, said there was no ash on the Whakapapa Skifield Road this morning and both the Whakapapa and Turoa skifields would open on schedule this morning.
The manager of the Chateau Tongariro, Tony Abbott, said there were about 100 skier guests at the hotel last night.
"It's business as usual here," Abbott said.
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