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Flights over New Zealand could be disrupted for days as ash from the Chilean volcanic eruption drifts across the country.

The Puyehue-Cordon Caulle volcano in Chile began erupting on June 4, with the ash plume drifting thousands of kilometres across the South Atlantic, South Africa, Indian Ocean, Tasmania and now across New Zealand.

It forced the cancellation of more than 60 New Zealand flights and left more than 7000 passengers stranded over the weekend.

Air NZ to continue flying

Air New Zealand were today continuing to fly but at lower altitudes to avoid cancelling or delaying flights.

But Jetstar and Qantas have cancelled a number of their trans-Tasman and domestic flights as a safety measure, with all checkout counters at Auckland International Airport closed this morning.

A Qantas spokeswoman said all trans-Tasman flights would be grounded until at least midday, when the situation would be reassessed.

Jetstar cancellations

Jetstar has cancelled 24 domestic and international flights today, including one flight from Auckland to Singapore and one flight from Singapore to Auckland.

Air NZ spokeswoman Tracy Mills said the national carrier would continually reassess the situation.

She said the company was adjusting flight routes and altitudes to ensure aircraft remained clear of any ash.

Cloud could cover North Island tomorrow

Civil Aviation meteorologist Peter Lechner told NZPA the cloud could be over most of the North Island by tomorrow morning, which would affect airline operations.

To people on the ground the ash particles, which were finer than house dust, would appear as high, thin cloud.

"You can imagine how much volume of air is being sucked through a jet engine, you can accrue a lot of ash, and the turbine blades are very hot so it just sticks to the blades, melts and builds up and eventually stalls the engine."

The ash was at an altitude of between 6000m and 10,700m.

Jets normally cruised between 8000m and 9800m, and turboprops operated at between 5500m and 6100m.

Aircraft could operate under that band safely, although jets would use more fuel at lower altitudes, making it more expensive for the airlines, Mr Lechner said.

Civil Aviation Authority spokesman Bill Sommer said the volcano was still ejecting particles, so further plumes could shroud the country until the eruption was over.

Unlike overseas aviation authorities, the CAA does not have the power to ground planes, and can only advise airlines.

When the volcano first erupted on June 4, ash was thrust 15,000m into the air, which meant the particles travelled through the stratosphere without being broken up by weather patterns.

It has since travelled 9000km over Argentina, Uruguay, South Africa and Australasia and is expected to circumnavigate the globe by the end of the week.

New Zealand is particularly vulnerable to the plumes because it lies on the same latitude as Chile. The westerly band of trade winds known as the "Roaring Forties" moves quickly, because there is little land south of 40 degrees. These winds have pushed the ash cloud directly towards New Zealand before it has had time to diffuse.

The volcanic ash can lead to a loss of thrust or engine failure - known as "flame-out" - on planes.

The ash can also wear down engine parts and clog fuel and cooling systems.

- with NZPA