Police and LandSar crews are urging potential hikers of one of the country's most popular treks to ensure they're prepared for the conditions.

Six adults and a 2-year-old suffering hypothermia have recently needed rescuing from the challenging track.

Senior Constables Barry Shepherd of Taupo and Conrad Smith of National Park Police today expressed their frustration about people taking on the crossing with inadequate food and clothing and poor fitness levels.

"In the last two weeks Police and LandSar in the Central North Island have rescued numerous people off Mt Tongariro.

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"The forecast for this week includes snow down to 700m, which means it will be extremely cold in the mountains and there is a high risk of hypothermia if ill prepared.

"Last weekend two people were rescued and the previous weekend nine people were rescued within Tongariro National Park.

"One of the rescues was a group of six adults and a 2-year-old child. When found some of them were suffering from hypothermia, and rescuers thought they would have died if we did not get to them."

Further cold weather is planned so the constables are urging trampers to keep tabs on ever-changing weather conditions.

"You need to plan and prepare for alpine hikes.

"If the weather is not favourable, do another activity, don't risk your life."

Some people did not understand the weather risks associated with hiking in an alpine environment, they said.

"The Tongariro Alpine Crossing is not a casual walk in the park - it is an alpine crossing in a volcanic environment that requires a high level of fitness and understanding of weather conditions.

"If it's raining and cloudy down low, it is likely that the scenic views will be obstructed, and it will be wetter and even colder at altitude – it's not fun hiking in cold, wet conditions and there are often much safer and still enjoyable alternatives, which can be recommended by i-site or DoC visitor centres."

The summer season for hiking the Tongariro Alpine Crossing ends this month as the increased frequency of snow will bring avalanches and hazardous icy conditions.

The Department of Conservation will be recommending winter visitors go with a guide.