Defence Minister Kevin Andrews has said Australia will continue to fly military aircraft over disputed waters in the South China Sea even if Beijing imposes a unilateral restricted air zone.

A day after demanding an end to Beijing's island-building in the contested waters during a key Asian security conference, Mr Andrews indicated Australia would not heed any "air defence identification zone", which Beijing has reserved the right to declare.

Any such zone, which would require aircraft to request permission to fly through the airspace, would be regarded as a great provocation in the tense stand-off over Beijing's increasing assertiveness over the Spratly Islands, which are also claimed by Malaysia, the Philippines, Vietnam and other neighbours.

"Our view is, as a matter of principle, that international transit passages whether on the sea or in the air should remain free and open for access to any country to legitimately use that, particularly for trade purposes," Mr Andrews told Fairfax Media on Monday.