Qantas spokesman David Epstein says passengers should prepare for significant disruption with the volcanic eruption in Iceland grounding flights across Europe in the biggest air travel shutdown since World War II.
"At this stage it's highly unlikely things are going to return to normal for several days at least, and it may well be a week," Mr Epstein said on Saturday.
Thousands of Qnatas passengers stranded
About 2000 Qantas customers in Asian ports are being given the option of onward flights to other destinations or flights back to Australia.
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The national carrier estimates 8000 Qantas customers have been impacted by the eruption, while about 100 international passengers stranded in Australia are being accommodated in Sydney hotels.
Mr Epstein said five daily flights usually bound for Europe on Saturday would proceed to Asian stopovers but not to onward destinations.
"It's a question of making a judgment not just when the airspace is open but when the airports are actually capable of taking our flights in and out in a way that doesn't disrupt passengers too much."
The backlog of customers would be accommodated as much as possible, Mr Epstein said, including flexibility with fares and rescheduling.
Qantas' meteorological unit tracks volcanic activity 24 hours a day, Mr Epstein said.
Safety before schedule
"It's best to put safety before schedule and where there's any question of volcanic ash being in the air we would prefer to take the safe approach rather than risk it to get flights in."
The Air Transport Association in Geneva estimates the current cost of the eruption to major airlines at around $US200 million ($A214 million) each day.
An Emirates spokesperson said passengers were urged not to go to airports before establishing the status of their flights.
"Emirates is keeping its flying schedule under constant review and will aim to give customers as much notice as possible once more information is received from European Air Traffic Control authorities," the spokesperson said.
Singapore Airlines spokeswoman Susan Bredow told AAP all passengers stranded in Singapore would be brought home free of charge.
"We're going to bring everyone home as soon as possible," she said.
Flights started bringing passengers back to Australia on Saturday and passengers were being re-booked with a five-day delay anticipated.
Anyone booked on a Singapore Airlines flight to Europe is urged to contact 13 10 11 for more information.
