The Australian plane was flying a "routine" surveillance patrol over the contested waters on February 11 when a Chinese fighter jet approached, the defence department said.

The Shenyang J-16 strike jet "released flares in close proximity" to the Australian Poseidon surveillance plane, the department said.

"The Australian Government has expressed its concerns to the Chinese Government following an unsafe and unprofessional interaction with a People's Liberation Army Air Force aircraft.

"This was an unsafe and unprofessional manoeuvre that posed a risk to the aircraft and personnel."

The mid-air incident is the latest in a string of episodes between China and Australia in the increasingly contested airspace and shipping lanes of Asia.

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.

The divers had been sailing on an Australian navy frigate, the HMAS Toowoomba, tasked with supporting sanctions enforcement efforts in Japan's exclusive economic zone.

"Australia expects all countries, including China, to operate their militaries in a safe and professional manner," the defence department said on Thursday.

"For decades, the (Australian Defence Force) has undertaken maritime surveillance activities in the region and does so in accordance with international law, exercising the right to freedom of navigation and overflight in international waters and airspace."