Australian airline Qantas cancelled 18 flights Tuesday and warned of further possible disruption after aircraft engineers walked off the job.

The engineers have staged rolling stoppages Monday and Tuesday at Sydney, Melbourne, Brisbane and Cairns airports demanding a five per cent wage increase, and have threatened to extend the strike action until Thursday.

"We have currently cancelled 18 flights. However, we are saying that more cancellations and consolidation may be required as the day progresses," a Qantas spokeswoman said Tuesday morning.

Some international passengers experienced six-hour delays Monday, but Qantas chief executive Geoff Dixon said major domestic routes, such as Sydney to Melbourne, were the worst affected.

Dixon said Qantas was determined not to back down in the dispute, even though the airline was on track to post record profits, since it would also have to pay an extra two billion Australian dollars (1.9 billion US dollars) for fuel next year.

"Everybody, apparently except the engineers, realises that fuel is almost out of control, that all airlines around the world are making major changes to their business and we have to do the same," he told ABC radio.

He said the airline would consider using non-union engineers in Australia during the dispute, but added Qantas was not seeking to break the unions.

"We're not going to lock people out, we're not going to try and change our workforce -- that is not on," he said.

"This will be resolved one way or the other but I think it's very, very important that it's resolved so Qantas has a secure future."