The nation's two major airports face the prospect of being shut down for up to 48 hours as the ash cloud from a Chilean volcano continues to drift across southern Australia.

Thousands of passengers have been stranded as the lingering cloud forces airlines to cancel some domestic and international flights.

Transport Minister Anthony Albanese says the Federal Government backs the cancellations in the interests of safety.

He says the Civil Aviation Safety Authority (CASA) and Airservices Australia are working with the airlines to ensure safety procedures are being followed.

Mr Albanese says the Bureau of Meteorology estimates Adelaide will be affected for 24 hours, Canberra and Sydney for around 36 to 48 hours, and Melbourne for 36 to 48 hours from tomorrow morning.

The ash cloud from Chile's Mount Puyehue Cordon Caulle volcano is circling the Earth for a second time, after last week delaying flights across Australia and New Zealand for several days.

CASA spokesman Peter Gibson says he hopes the ash cloud will have dissipated by then.

"Obviously we've got hundreds of thousands of passengers today disrupted right around the country," he said.

"When you take out major centres like Sydney and Melbourne, the knock-on effects of that are huge, and that's unfortunate, but safety has to come first.

"When it's safe to go flying, the airlines will go back, but not until then."

Virgin's domestic cancellations alone affect 170 flights and 120,000 people.

Virgin spokeswoman Danielle Keighery says all flights from Canberra were to cease from 1.00pm, and the cancellations will also affect Port Macquarie, Coffs Harbour and Newcastle from 4.00pm.

"The ash plume is at a very low level. Last week we cancelled operations where the plume was low, and we are seeing that again," she said.

"We are hopeful it won't last long, but it is a moving feast."

The ash cloud earlier forced the cancellation of all domestic flights to and from Adelaide for the day.

Flow-on effect

Brisbane Airport Corporation (BAC) has said delays are likely, and spokeswoman Leonie Vandeven says travellers should keep in contact with their airline for any changes.

"Quite simply if Sydney Airport sneezes, we're going to catch the cold, so we're expecting some significant delays into and out of Brisbane airport," she said.

"We're not sure what's going to be happening with this volcanic ash cloud other than it will be affecting us if it's affecting flights in other states."

In Sydney, one passenger aiming to get to Port Lincoln said he had been waiting for hours.

"The original plan was to fly out early this morning to Adelaide and then drive to Port Lincoln, but obviously we couldn't get to Adelaide," he said.

"I left home at 3.00am and I can't get anywhere, can't get to Adelaide, and I'm pretty much camping out waiting for news.

"We asked to be transferred to a 5.00pm flight this afternoon but they told us that they're not accepting any bookings, so we're here until we can get on a flight pretty much."

Another traveller trapped in Melbourne said he checked the Tiger website before leaving for the airport, but no information was available.

"We checked the website and we didn't see anything on the website," he said.

"It seems everyone else is flying. I don't know why they're not."

Alternative transport

Other travellers were happy with the response by airlines.

"What can you do - safety first I reckon," one traveller said.

"It's disappointing, but all things considered it's better to have it like this than have it crash because of the ash," another traveller said.

The flight disruptions have had knock-on effects in the west, with many passengers in limbo and unable to reach Perth due to a lack of connecting flights.

Bus company Greyhound Australia say it expects services to triple over the next two days.

The company says it is putting on extra services for people affected by the ash cloud.

The head of Greyhound, Tony Hopkins, says extra services will operate between Adelaide, Melbourne, Canberra, Sydney and Brisbane.

Mr Hopkins says the extra services will run until the ash cloud passes.