Scientists are worried cooling temperatures in the Mount Ruapehu crater lake may result in a minor eruption.
The GNS Science volcanic alert level was still at its normal level of one, but the Conservation Department was taking precautions.
The lake had been at 15 degrees for the last two weeks, which could be a sign that the magma, which heats the lake, has a blockage and was restricting the heating process.
DOC was warning people to stay at least 400 metres away from the lake and avoid camping in the summit area and lingering in the Whangaehu and Whakapapaiti valleys.
"Eruption Detection Systems on the mountain are fully operational and other precautions have been taken at the Far West T-bar area," DOC's Volcanology Advisor Dr Harry Keys said.
He said advisory signs were being erected at the top of Whakapapa and Turoa ski areas and the Tukino Road end.
Mr Keys said they were being cautious in case there was a blockage, but he believed GNS test results wouldn't be alarming.
DOC and GNS were continuing to monitor the situation, and were gathering more information from the Crater Lake.
The ski fields and roads in the area were not affected at this stage.