An increase in volcanic activity has led to a rise in White Island/Whakaari's alert level.
The island now has an alert level of two, with an aviation colour code of yellow.
The level-two warning signifies "moderate to heightened volcanic unrest" according to Geonet.
The highest level on the scale is five, which is only given during a major volcanic eruption.
"In the past few weeks, the level of volcanic tremor has also increased from weak to moderate strength," Geonet said.
The higher alert level comes after an increase in the amount of SO2 gas coming from the island.
"The SO2 gas originates from magma (molten rocks) at depth and the longer-term data from the past few months suggests a possible increase in gas passing through the volcano from depth," Geonet said.
The volcano's crater lake has been slowly rising since August, with a weak geyser-type activity observed at the edge of the lake. However, other measurements made on the island show no significant changes, Geonet said.
The current activity is similar to that seen from 2001 to 2016 and "suggest that Whakaari/White Island may be entering a period where eruptive activity is more likely than normal".
White Island has been volcanically active at least since it was first spotted by James Cook in 1769. Sulphur mining was attempted on the island but abandoned in 1914.
