The Volcanic Alert Level has been increased to Level 3 and the Aviation Colour Code raised to orange.
On Geonet's website, duty volcanologist Geoff Kilgour said the volcano had produced "a more vigorous plume" this afternoon, moving volanic ash to the east of the island.
"There is a low probability of this ash affecting the mainland. This weak eruptive activity was identified through a combination of webcam imagery and satellite data provided by our colleagues from the Volcanic Ash Advisory Centre at NZ MetService.
"The activity appears to have been most active from around 1 to 3 pm and has since diminished. Satellite data shows that the plume appears to have contained a minor amount of volcanic ash."
Kilgour said the volcano was currently experiencing a period "of elevated unrest".
Steam and ash emissions "could continue for some time".
In 2019, 22 people died and 25 others were injured when the volcano - a popular tourist site - erupted.
