The volcanic alert level for Mount Ruapehu has been raised, signalling a higher chance of an eruption.
GNS scientists said there was more gas coming from the crater lake, levels of tremor were continuing and the lake temperature was high.
The volcanic alert level was moved from level one to two - moderate-to-heightened unrest - with a spokesperson saying there was now a heightened potential for an eruption from the volcano.
The warning to aircraft flying near Mt Ruapehu had also been raised to yellow, indicating signs of activity had been detected.
The scientists made two monitoring visits to Mt Ruapehu yesterday, and said they would continue to keep a close eye on it.
Climbers and trampers have been warned by the Department of Conservation to stay out of the summit hazard zone until further notice.
However, GNS volcanologist Geoff Kilgour said the likelihood of Mt Ruapehu erupting was still low.