Scientists have deemed there's now a greater likelihood of Whakaari/White Island - off Bay of Plenty - erupting.
The volcanic alert level for the island has been raised to level 2 by GNS Science.
The aviation colour code has been raised to yellow.
Sulphur dioxide levels are at their highest levels in six years.
In a statement GNS Science say they've raised the alert level because of an "increase in sulphur dioxide gas flux to historically high levels".
During a flight today 1886 tons/day of sulphur dioxide was detected. This is nearly three times the previous values measured in May.
It's the highest value recorded since 2013 and the second highest since regular measurements began in 2003.
GNS Science says: "Nearby earthquake swarms are continuing although at lower levels [than previously]. It is still unclear of the relationship of the earthquake swarms to the high sulphur dioxide observed today.
"The change in gas flux represents a significant change in our background monitoring parameters at Whakaari and is consistent with moderate or heightened volcanic unrest."
GNS Science say they continue to closely monitor the island for further signs of activity, along with the National Geohazard Monitoring Centre.
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