The alert level for Mt Ruapehu has been raised a notch as the volcano continues to show signs of life and climbers have been warned to stay clear of its summit.
Government scientists have lifted the volcanic alert level to reflect the rise in gas output from the crater lake, a high lake temperature and continued seismic activity.
It now stands at level two which indicates moderate to heightened unrest.
"The increased gas output coupled with high heat flow and volcanic tremor imply a higher likelihood of activity," says duty volcanologist Geoff Kilgour.
GNS scientists have also raised the aviation colour code from green to yellow to reflect the higher level of volcanic unrest.
The Department of Conservation warned people to remain outside the summit hazard zone - an area within 2km of the centre of the crater lake.
"We recommend climbers, trampers and walkers do not enter the zone," says DOC's Paul Carr.
Ski areas and roads on the mountain were not affected but trampers were advised to be aware of an increased possibility of lahars.
The Tongariro Alpine Crossing was not affected by the warning.
Measurements taken yesterday revealed an increase in carbon dioxide and sulphur dioxide on Mt Ruapehu.
The temperature of the crater lake was ranging between 45C-46C in recent days and has risen by 20C since mid-April.
There has also been an increase in volcanic tremors on the 2797m mountain after a swarm of earthquakes late last month.
Volcanologists will continue to closely monitor Mt Ruapehu, which had its last major eruption in 2007.