Three Chinese navy vessels -- a frigate, a cruiser and a supply tanker -- were spotted last week in waters off mainland Australia.

They have since charted a course taking them down Australia's eastern coast.

"We are keeping a close watch on them, and we will make sure we are watching every move," Defence Minister Richard Marles told Sky News.

"It's not unprecedented. But it is an unusual event."

Marles stressed the vessels were "not a threat" and that they were "engaging in accordance with international law".

Canberra rebuked Beijing last week for "unsafe" military conduct, accusing a Chinese fighter jet of dropping flares near an Australian air force plane patrolling the South China Sea.

Beijing swiftly hit back, accusing the Australian plane of "violating Chinese sovereignty and endangering Chinese national security".

It was the latest in a string of tense encounters between China and Australia in the increasingly contested airspace and shipping lanes of the Asia-Pacific region.

A Chinese fighter jet was accused of intercepting an Australian Seahawk helicopter in international airspace in 2024, dropping flares across its flight path.

In 2023, a Chinese destroyer was accused of bombarding submerged Australian navy divers with sonar pulses in waters off Japan, causing minor injuries.