An increase in gas output has been recorded through the crater lake (Te Wai ā-moe) at Mt Ruapehu - in particular of carbon dioxide (CO2).
An airborne gas flight on Monday confirmed there had been an increase in the CO2 output, with it being recorded as the second-highest value ever.
GNS Duty volcanologist Brad Scott said the nature of the volcanic unrest differs from what is usually seen at the start of a heating phase.
"The volcanic tremor signals and elevated gas output are now more indicative of processes being driven by molten rock (magma) interacting with the geothermal system at depth in the volcano."
The changes indicate magma may now be the reason for the unrest increasing the chances of further activity.
Mt Ruapehu's volcanic alert level was raised to alert level two and the aviation colour code was changed to yellow in March after Te Wai ā-moe's temperature increased from 32C to 36C.
The current temperature of Te Wai ā-moe is 38C.
Scott said although the likelihood of the volcano erupting is still low, there remains a chance it could erupt.
"There is also a possibility of a single or multiple eruptions that could impact the summit area and generate lahars into some catchments draining off the volcano, especially the Whangaehu Valley."
Volcanic Alert Level 2 is to indicate hazards such as volcanic gas, earthquakes, and hydrothermal activity.
Although Volcano Alert Level 2 is mostly associated with volcanic unrest hazards, eruptions can still occur with little or no warning.
GeoNet will continue to monitor the volcano for any further changes.
