Farmers in the central North Island are being warned to prepare a plan to deal with volcanic ash settling on their pasture.
Monday night's eruption from Mt Tongariro sent a sizeable fine ash cloud across northern Hawke's Bay.
Hawke's Bay Civil Defence says it has left a layer of ash about 1mm deep in some areas inland from Napier and north-east into the Wairoa area.
Federated Farmers says farmers have so far reported minimal impact on pasture or stock drinking water.
But GNS Science is warning there could be further eruptions and Federated Farmers Rotorua Taupo president Neil Heather says lessons were learnt during the Ruapehu eruption in the mid-1990s.
He says farmers should give stock alternative feed until rain has washed pasture clean, and flush out animal drinking troughs.
Civil Defence is also advising people in the path of the ash cloud to disconnect downpipes from water tanks, gully traps and gutters to prevent blockages and allow ash to empty onto the ground. That will also help protect the water supply of those relying on rainwater.
Householders are advised to hose off their roofs before reconnecting pipes after the ash has cleared.