Australia is in for round 2 of the menacing Chilean ash cloud.

Thousands of air passengers will be left stranded as flights to and from South Australia are cancelled due to volcanic ash from Chile's Puyehue volcano again this week.

Qantas has cancelled 25 flights into and out of Adelaide and Port Lincoln airports between 6:30am (ACST) and 2:00pm after getting away five flights early this morning. The airline plans to reassess the situation this afternoon.

Budget airline, Tiger Airways announced that all flights around Australia have been cancelled until at least 2:00pm local time and Jetstar has cancelled selected flights, while Virgin has grounded flights involving Adelaide for the duration of the day.

Contrary to their stance last week, Virgin spokesman Colin Lippiatt says the airline has been advised it is not safe to fly underneath the ash cloud, according to ABC News.

Tristan King, a meteorologist with the Volcanic Ash Advisory Center in Darwin, Australia, said on Monday that if the ash stays on its current course (and doesn't dissipate) it could eventually disrupt air traffic in Sydney, Melbourne, and the country's capital, Canberra.

The ash cloud is forecast to descend below 20,000 feet (6100 meters) and affect flight paths.

On the bright side, experts in Chile said on Sunday that the Cordon Caulle volcano, which began erupting on June 4, is becoming less active.

Curious why airplanes can't fly through ash? Read about it here.

Want to see photos from the initial eruption? View them here.