An ash cloud created by a volcanic eruption in Chile more than two weeks ago was again set to disrupt flights in Australia after looping the globe and returning Down Under, forecasters said Monday.

The Puyehue volcano's activity has been steadily decreasing, permitting people to return to their homes in the Andes mountains, but the huge ash cloud it ejected is still floating over the southern hemisphere.

Andrew Tupper, head of the Australian Bureau of Meteorology's Volcanic Ash Advisory Centre, said while the ash had thinned during its travels it was still expected to impact on southern Australian airspace on Tuesday.

"Although much of the ash that came around us last week has dissipated the leading edge of it... is coming around for another shot," he said.

"We are seeing it really very clearly on satellite imagery."

Tupper said the cloud was about 2,000 kilometres (1,240 miles) south of Western Australia, but was expected to cross the southeastern coast and affect Adelaide airport early Tuesday. It is also likely to affect Melbourne, he said.

He added that it was too soon to know whether it would affect the country's busiest airport Sydney, but admitted the cloud would be an "uncomfortably close" distance of about 100 kilometres from the hub.

The cloud, which is travelling at an altitude of 8-13 kilometres, was generally at cruising level and this could cause disruptions for aircraft.

"It will obviously cause disruption, it will obviously prevent aircraft flying at the altitude of the cloud," Tupper said. "How they choose to cope with that is their decision."

The cloud entered Australian and New Zealand airspace just over a week ago, causing some airlines to ground all flights to affected areas whereas others chose to divert their planes under and around the plume.

The ash disrupted the travel plans of tens of thousands of people in Australia and New Zealand, cancelling most trans-Tasman travel and disrupting flights to Melbourne, Adelaide, Perth and Hobart.

Tupper could not say how long the new ash front would last, but said it would probably linger over any one place for only a day.

Ash poses a significant threat to aircraft because once sucked into engines it can be converted into molten glass as a result of the high temperatures and potentially cause an engine to fail.

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