The rumblings of Mt Ruapehu are thought to have been a one-off, rather than the beginnings of a major eruption.

The Department of Conservation has downgraded the risk warning from high to medium after last week's hydrothermal eruption.

DOC scientist Harry Keys says the event and its effects were contained to the crater basin. He says seismic activity is back to normal and there are no signs of magma movement or an imminent eruption.

Dr Keys says it must be remembered that Ruapehu is an active volcano and climbers should be careful in the region.