Seismic activity has increased at Mt Ruapehu after the lake in the volcano's crater peaked in temperature.
Tremors under Mt Ruapehu have been occurring at a "higher than normal rate", according to GNS volcanologist Brad Scott.
Scott said an increase in volcanic tremor at Mt Ruapehu began on October 18, where a "sharp increase was noted before the energy declined a day later".
Mt Ruapehu's Crater Lake had been heating at a rate of 1C per day until it reached a peak of 40C on October 4. It has since cooled slightly and is now about 37C.
Tremor increases happened again on October 25 and 28, and the intensity of the tremor remains higher than normal.
Scott said the tremor increase does not seem to be related to a change in the lake temperature, and similar increases in volcanic tremor were present in May and June this year.
"No eruptive activity or geysering was noted in Crater Lake during the previous periods of volcanic tremor."
Scott said weather conditions have hindered observations of the mountain but scientists will be heading to the mountain when conditions allow it.