The westward-blowing cloud of fine ash spans altitudes between 20,000 feet and 35,000 feet, Meteorology Manager Peter Lechner of the Civil Aviation Authority told Radio New Zealand.
Except for the very northern tip of Northern Island, the entire country was under the cloud and would be for the foreseeable future, he said.
Lechner said even if the Puyehue Cordon Caulle volcano were to stop erupting Sunday, the existing ash cloud would take almost a week to dissipate.
The volcano sprang to life June 4.
The ash has created mayhem for the airline industry in New Zealand, Tasmania and Australia, the report said.
Jetstar said it had grounded all of its domestic and Australia flights, which affected 6,000 passengers in New Zealand and 2,000 in Australia.
Qantas, Pacific Blue and Emirates also canceled domestic and flights to Australia, the report said.
The volcano has also disrupted air travel in Argentina, Uruguay and Brazil, officials in those countries said.