Scientists are warning that heavy rain could trigger more mudflows from Mt Tongariro, which continues to vent gas and steam since last Monday's eruption.
After heavy dowpours on Sunday morning, streams of muddy water flooded State Highway 46, about six kilometres west of Rangipo.
GNS Science volcanologist Michael Rosenberg says rain-triggered mudflows, called lahars, are common after eruptions because of loose ash and debris in stream catchments.
