The GeoNet monitoring service said White Island, an uninhabited landmark off the North Island’s Bay of Plenty, erupted at 10:23am (2223 Monday GMT).
“The eruption appears to have continued for about 10 minutes and mainly produced steam,” it said, issuing an aviation warning for the area around the island but reporting no damage.
The volcanic activity is not believed to be related to a 6.5-magnitude earthquake which rocked Wellington Friday on the other side of the North Island.
New Zealand has a number of active volcanoes.
Mount Tongariro, in the middle of the North Isand, rumbled to life on two occasions last year after lying dormant for more than a century, spewing out clouds of ash that disrupted air traffic.
An eruption at Mount Ruapehu in 1953 caused New Zealand’s worst rail disaster when it trigged a massive mudslide that washed away a bridge, causing a passenger train to plunge into the Whangaehu River with the loss of 151 lives.