Ash from the Tongariro eruption overnight has coated farms east of the mountain in ash several millimetres thick.
Westerly winds have pushed the ash cloud eastward into sparsely-populated areas in the Hawke's Bay.
Civil Defence says the volcanic activity could pose a threat to Waikato, Hawke's Bay, Gisborne, Manawatu, Wanganui, Bay of Plenty and Taranaki.
Watch the video for footage taken of ash-covered land from the air.