GNS Science has issued a volcanic alert for White Island in the Bay of Plenty, due to signs of increased activity.
The aviation alert code has been lifted by GNS from green to yellow, which is when a volcano is showing signs of elevated unrest.
Michael Rosenberg, GNS Science duty volcanologist, said its crater lake has started to re-fill and gases were now "vigorously streaming through it".
"Airborne gas measurements made yesterday show that the discharge of some sulphur gases has increased.
"During the past few weeks there has also been some minor volcanic tremor," GNS said.
Rosenberg says between July 27 and July 28 the crater lakes level rose by about 3m to 5m.
And a recent ground survey also shows that the main crater floor may be slowly rising, he said.
Rosenberg said the phenomena was "typical for White Island's activity, but are the first substantial changes to occur in the last few years".
"White Island is an active volcano and there is always risk when visiting the island. Eruptions can occur at any time with little or no warning," he said.
He said the increased activity at White Island has no connection with the recent earthquakes and changes in gas flux at Tongariro volcano.
GNS advises people to take extra caution, especially if approaching the crater lake and other active thermal features.