GNS Science has raised the aviation alert for White Island to the second highest level, warning that explosive eruptions could occur at any time.
GNS said on Thursday that volcanic unrest has increased and as a result the Aviation Colour Code alert has been upgraded to orange.
It says a type of earthquake is occurring that is typically associated with the movement of magma within an active volcano.
Volcanologist Gill Jolly said the activity on the Bay of Plenty island is some of the most vigourous for many years and explosive eruptions could occur at any time with little or no warning.
Ms Jolly said a high level of caution should be taken if visiting the island.
The effects of volcanic gas exposure include respiratory issues and skin and eye sensitivity to acid gases.