Flights cancelled and major roads closed
Witnesses reported dramatic scenes, with bright flashes and a pillar of steam and ash billowing into the air, as Mount Tongariro burst into life just before midnight local time.
The eruption of the 6,490ft volcano, one of three in a chain at the center of the North Island, took seismologists by surprise.
A large ash cloud covered an area of the central North Island throughout the day on Tuesday, closing airports at Palmerston North, Napier, Taupo and Rotorua.
For a time two main roads were also shut because of falling ash, including the Desert Road, a stretch of the highway that links the capital Wellington with Auckland, the country’s biggest city.
One of the first people to see the eruption was long-distance lorry driver Bryn Rodda, who was passing the mountain at the time.
“As I was coming up from Waiouru, I saw this beautiful, big cloud and I thought ‘gee that looks like a volcanic plume’.
“Just as I thought that, there was a great big orange flash,” he told National Radio.
David Bennett, a local resident, also saw the eruption and said rocks were being thrown out of the volcano.
“There were rumbling sounds, and thunder and lightning coming out from the base of the eruption.”
Some frightened residents fled their homes overnight, though no evacuations were officially ordered.