The Mountain Safety Council says some trampers attempting the Tongariro Crossing are unbelievably ill-prepared.
Programme manager Chris Tews says he knows of walkers wearing jandals and T-shirts, carrying only a shopping bag and an umbrella on the Crossing, in the Tongariro National Park.
Mr Tews says the 19km trail enters alpine territory in some parts and conditions can change from fine to icy, very quickly.
Up to 1000 people per day attempt the Crossing in the height of summer and Mr Tews says too many of them treat it casually.
Some $250,000 was spent on rescues in the central North Island in the year to June, much of it on the Tongariro Crossing.
Tongariro National Park was the first national park in New Zealand. It was established in 1887.