A minor volcanic eruption has occurred on White Island, 50km off the coast of Whakatane.
GNS Science said minor volcanic ash had been "passively emitted from a vent" on the 2012 lava dome. A report from the island at 11.50am confirmed the ash emission.
The alert was raised from level 1 to level 3. But there is no threat to public safety.
MetService released satellite images showing the eruption.
GNS Science said some of its cameras on the ground were affected by ash and steam so it might not be possible to see much from them in the short term.
However, it confirmed seismic activity was low on the island.
GNS Science volcanologist Brad Scott expected any further eruptions in the next few days to be similarly minor.
It was unlikely the activity was related to recent earthquakes in the North Island, he said.
"It's a rule of thumb not to connect volcanic activity to earthquakes. There are a lot of earthquakes which result in no eruptions."
It was difficult to know what would happen at the island in the mid term.
GNS staff visited White Island last week and found the crater lake was reforming and growing.
A steam and gas eruption on April 27 that could have killed anyone standing close to the floor of the Crater Lake created a new crater, caused landslides and removed 13m-15m of lake floor sediments.
Back in 2012 on December 12, GNS scientists raised the alert level to two at White Island after a 20-30m wide spiny lava dome was observed in a small crater.
A lava dome forms when magma, which has lost much of its gas, bubbles out of the crater of a volcano. It cools quickly and builds up from the bottom.
The scientists likened it to "congealed toothpaste" found round the edge of the tube.
It was the first time a lava dome had been observed at White Island. It was believed it had formed as a result of an eruption recorded on August 5 that year.