As a cloud of ash from an erupting volcano in Chile prompted cancellation of some domestic and international flights from New Zealand and Australia on Monday, authorities said flights could remain affected all week.

“The plumes are expected to be at cruising levels for both jet and turboprop aircraft (20,000 – 35,000 ft), but at the moment not below 20,000ft. Given that the volcanic activity is continuing, it is expected that New Zealand airspace may be affected by these plumes for at least a week,” Civil Aviation Authority (CAA) of New Zealand said in a statement.

The volcano in the Puyehue-Cordon Caulle chain in Chile began erupting on June 4 and has wreaked havoc on air travel since then in South America, as ash plume from the volcano initially reached as high as 50,000ft in the atmosphere.

On Monday, the ash cloud drifted over the Pacific Ocean to lie over southern parts of New Zealand and Australia, snarling air travel in the region.

“Volcanic ash particles come in a range of sizes and while the biggest will fall to the ground quickly, very small particles take a long time to settle out of the atmosphere. This eruption ejected these small particles very high into the atmosphere, where strong winds have carried them great distances to the east,” CAA officials said.

The volcano, which is located in Puyehue National Park in the Andes of Ranco Province of Chile, was dormant for decades. The eruption forced evacuation of about 35,000 residents.