Australian flights grounded by the Chilean ash cloud gradually resumed Wednesday, but thousands of passengers face lengthy delays as airlines scramble to clear a massive backlog.
Hundreds of services were cancelled Tuesday in Sydney, Melbourne, Adelaide and Canberra but the threat of prolonged disruption eased as the plume from the Puyehue volcano eruption pushed out towards the Tasman Sea and New Zealand.
National carrier Qantas restored flights to and from the South Australian capital Adelaide before dawn, and they were followed by Melbourne.
Canberra and Sydney routes will begin operating again at 2:00pm (0400 GMT), including international flights, although the airline said delays were expected on overseas services into both Sydney and Melbourne.
Despite planes again being airborne, Qantas spokeswoman Olivia Wirth said they expected thousands of customers to be affected once again.
"There were a significant number of people delayed over the past 24 hours. There were around 20,000 yesterday and we expect that number to go to around 50,000 today," she told Sky News.
The airline will put on extra flights to work through the backlog of passengers, some of whom have been stranded for two days.
"The backlog will take a significant time to clear but we will be looking at putting on as many extra flights as we can," said Wirth.
"Fingers crossed, we won't be seeing this sort of thing again."
While mainland flights began, Qantas and Jetstar services to Tasmania and New Zealand were halted until further notice as the ash cloud moves south.
Virgin resumed flights from Adelaide, with other capital cities to follow from midday.
Air New Zealand, which has maintained most services by flying under the ash cloud, said all routes continued to operate as normal, but it was constantly monitoring the situation.
New Zealand Civil Aviation Authority meteorological manager Peter Lechner said the plume was expected to cover the entire country later Wednesday and due to slow-moving winds would linger for "at least a day or two".
"It will be at a height of 20,000 feet (6,000 metres), which provides plenty of scope to fly under the cloud," he added.
Ash poses a significant threat to aircraft because once sucked into engines it can be transformed into molten glass by the high temperatures and potentially cause an engine to fail.
The cloud first entered Australian and New Zealand airspace over a week ago, causing some airlines to ground all flights to affected areas while others chose to divert their planes under and around the plume.
The Darwin Volcanic Ash Advisory Centre's director Andrew Tupper said the plume was a rare occurrence and a third loop back to Australia was not likely.
Australian Transport Minister Anthony Albanese admitted that the flight chaos would come at a cost.
"There's no doubt there will be a significant cost to all the airlines, but also an economic cost (to the country as a whole) -- people are not flying into Australia," he said.
"This means lower revenues for the tourism industry."
According to JP Morgan estimates, the lost revenue for Qantas of a 24-hour stoppage could be up to Ausê15 million (USê15.9 million), while the Tourism and Transport Forum put the impact on the tourism sector at over Ausê10 million a day.
Qantas shares went into a trading halt Wednesday, pending an announcement on the company's financial outlook.