The Department of Conservation has re-drawn a 700-metre exclusion zone around Ruapehu, asking Kiwis not to visit Crater Lake.
In response to a GeoNet bulletin on Tuesday, DoC is advising visitors not to camp or stay overnight within 1.5 kilometres of the summit lake.
Tuesday's bulletin advised that the volcano has entered a "heating phase" with the lake temperature reaching 31 degrees Celsius. The volcanic lake goes through periods of heating and cooling.
While these are within normal ranges of fluctuation, the area remains at Volcanic Alert Level 1 or "minor volcanic unrest."
"Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of volcanic unrest," said GeoNet volcanologist, Craig Miller.