Wellington - New Zealand's active volcano Mount Ruapehu is showing increased signs of activity, the Department of Conservation (DOC) warned on Friday, but it held back from banning climbers on the 2,797-metre-high mountain which last erupted in September.

A statement said there was a higher than normal risk to people entering the hazard zone near the summit and increased gas concentrations from the 17-hectare crater lake, about 250 metres below the peak, would affect some people.

DOC said there was "an anomalous state of activity" on the mountain and while it was unclear if it indicated eruptions in the near future they could occur without warning.

The department did not raise its alert above the standard Level One. (dpa)