Australia's biggest airline, Qantas, is to scale back its international flights as the airline tries to rein in its fuel bill.

Qantas is slashing its services in a bid to manage the rising cost of oil which it says will add US$2 billion to its fuel bill next financial year.

Japan and South East Asian flights are the worst affected in the latest round of cuts, which will see a complete overhaul of flights between Cairns and Japan.

About 40 pilots based in Cairns will return to other bases, and there will be job cuts there and in Japan.

The changes begin later this year and include the withdrawal of the Melbourne to Tokyo return service and a reduction in Sydney to Tokyo, and Sydney to Los Angeles flights.

Jetstar will takeover Qantas on some routes including Perth to Denpasar and Perth to Jakarta.

Qantas has already announced domestic flight cuts, with several hundred jobs to go.