The Australian Poseidon was flying a surveillance patrol over the South China Sea on Sunday when it was approached by a Chinese fighter jet, Australia's defence department said.

The Chinese jet released flares in "close proximity" to the Australian aircraft, the defence department added, endangering the crew onboard.

It was the latest in a string of episodes between China and Australia in the increasingly contested airspace and shipping lanes of Asia.

"Having reviewed the incident very carefully, we've deemed this to be both unsafe and unprofessional," Defence Minister Richard Marles told reporters.

Marles said Australia had raised the encounter with Chinese diplomats in both Canberra and Beijing.

Australia would continue to conduct freedom-of-navigation exercises in the region, Marles added.

A Chinese fighter jet was accused of intercepting an Australian Seahawk helicopter in international airspace last year, 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.

China claims almost all of the South China Sea, despite an international ruling in 2016 concluding this has no legal basis.