Tens of thousands of travellers were stranded Monday after ash from Chile's volcanic eruptions prompted Australian airlines to ground some domestic and international services.
Strong winds have carried the ash more than half way around the world, over the southern Atlantic and southern Indian Oceans to Australia and as far as New Zealand since Chile's Puyehue volcano erupted more than a week ago.
Qantas said all flights in and out of the southern island of Tasmania and to New Zealand remained grounded Monday, but it lifted a ban on flights to and from the southern Australian city of Melbourne.
The ash has already forced the cancellation of several international flights from airports in Argentina and Uruguay, and Qantas said three international services to Buenos Aires and Los Angeles were also halted.
A total of 110 Qantas flights were cancelled on Sunday and Monday, delaying at least 20,000 travellers while as many as 25,000 more passengers have been disrupted by Qantas's offshoot Jetstar suspending some flights.
The airlines said it would take several days to work through the backlog, but it was too soon to say how long the ash would linger over Australia.
"It's down to our safety standards. Our Qantas group policy is that if there is any sign of ash cloud around we won't operate," airline spokeswoman Olivia Wirth told state broadcaster ABC.
Aviation authorities and airlines are closely monitoring the plume, with Virgin Australia saying Monday it believed it was safe to fly to Melbourne, Tasmania and New Zealand, adding its planes would fly around or under the ash.
When Iceland's Eyjafjoell volcano erupted last year, its vast ash cloud grounded more than 100,000 planes as authorities in Europe fretted over potential damage from the razor-sharp ash particles to jet engines.
But there are no official or industry-wide standards regarding volcanic ash and many European airlines, suffering hefty losses and grappling with millions of stranded passengers, were angered at their governments' caution.
In New Zealand, the Civil Aviation Authority (CAA) said the cloud now covered most of the country and was likely to remain for the next 24 hours.
Spokesman Bill Sommer said the authority believed it was safe to fly under the cloud, but the decision on whether to fly rested with individual airlines.
Air New Zealand said it had operated 473 flights on Sunday, carrying more than 26,500 passengers around the country and across the Tasman, after making changes to flight paths and cruising altitudes "to completely avoid the ash".
"It would have been far easier to simply cancel flights," chief pilot Captain David Morgan said.
The airline said to avoid the ash, trips to Australia had been given new flight paths heading further north than normal before crossing the Tasman, while domestic services were operating at a maximum 5,500 metres (18,000 feet).
Australia's Civil Aviation Safety Authority (CASA) said airlines were free to operate, provided they avoided areas forecast to hold volcanic ash.
"Airlines may chose to take a more conservative approach based on their own risk assessment," it said. "That is acceptable to CASA and is consistent with the approach taken by regulatory authorities in Europe."
The flight disruptions have affected holidaymakers, sports players and politicians alike, with the air force called in to fly Tasmanian lawmakers back to Canberra for the resumption of parliament on Tuesday.
Rugby league player Robbie Farah scrambled onto an Emirates flight out of Auckland after his surprise call-up to the New South Wales State of Origin squad, while his Wests Tigers teammates stayed in New Zealand.
Australia's Volcanic Ash Advisory Centre said a similar ash cloud had not been seen in the region in two decades and this one was likely to continue to travel around the globe.