Scientists are warning the crater lake on Mount Ruapehu is the hottest it has been for two years.
Mount Ruapehu as seen from entrance to Tongariro National Park Photo: RNZ / Kate Newton
GNS Science said today Te Wai ā-moe reached 42 degrees Celcius yesterday after rising by 0.5C per day for the last two weeks.
Only 1 percent of post-2009 temperatures had exceeded 42C.
GNS said the alert remained at level one - "minor unrest" - but warned eruptions could occur with little or no warning.