International flights have been cancelled as a volcanic ash cloud from Chile heads towards New Zealand.

Qantas cancelled transtasman services from the South Island today and Air New Zealand warned of changes to flight paths.

The cloud reached New Zealand a week after the Cordon Caulle volcano in Southern Chile erupted, sending plumes of ash more than 15,000m into the sky.

The ash caught a ride to our shores on a powerful band of wind known as the Roaring Forties, that has carried it east since the eruptions began.

Last night the ash had reached the western tip of the South Island, treating Southlanders to a deep-red sunset.

The Civil Aviation Authority expected it to reach skies above the rest of the country before daybreak today.

The cloud was circulating above 6100m, meaning most planes could avoid danger by flying lower than normal.

“A 737 will usually operate at about 23,000ft (7000m) so they will be able to fly but they will use more gas,” meteorologist Peter Lechner said.

Air New Zealand confirmed it would adjust routes and altitudes but did not foresee delays or cancellations.

However, Qantas last night cancelled several flights for today, including QF45 from Sydney to Christchurch, QF46 from Christchurch to Sydney, QF121 from Sydney to Queenstown and QF122 from Queenstown to Sydney.

The MetService will track the volcanic ash plumes and provide warnings to the aviation industry here and overseas.

The CAA said flights on transtasman routes, over the South Island and to South America were likely to be most affected.

Unlike overseas bodies, the CAA does not have the power to ground planes.

“We put the information out there and it’s up to the airlines to decide what to do,” spokesman Bill Sommer said.

He was confident airlines would pay close attention to advice.

Aircraft Owners and Pilots Association vice-president Don Ryder said volcanic ash was dangerous to fly through because it could cause engines on larger aircraft to seize.

It was unlikely to affect visibility, he said.

Image / WeatherWatch.co.nz

– Herald On Sunday, additional reporting NZPA