Australia has told China it has serious concerns about injuries to its navy divers by sonar pulses from a Chinese destroyer inside Japan’s exclusive economic zone this week.

A People’s Liberation Army-Navy destroyer ignored requests to keep clear of the divers, Defence Minister Richard Marles said in a statement on Saturday. They had been freeing nets that had become entangled around propellers of the Australian navy’s HMAS Toowoomba, which was conducting operations in the area on Tuesday to support United Nations sanctions.

“Medical assessments conducted after the divers exited the water identified they had sustained minor injuries likely due to being subjected to the sonar pulses from the Chinese destroyer,” Marles’ office said, calling the incident “unsafe and unprofessional conduct.”

Relations between Australia and China have rapidly improved over the past 18 months following the election of the center-left Labor government in Canberra. A visit to Beijing by Prime Minister Anthony Albanese earlier this month marked the first such trip by an Australian leader in more than seven years.

Read More: Australia-China Tensions Ease as Albanese Ends Beijing Trip

The Australian ship had been in the waters as part of Operation Argos, enforcing sanctions against North Korea during a regional presence deployment, the navy had earlier said.

Australia has accused China's navy of using sonar pulses in an incident in international waters that resulted in Australian divers suffering injuries.

The Australian defence minister said a Chinese warship had resorted to "unsafe and unprofessional" actions during the encounter off Japan earlier this week.

The warship approached an Australian frigate as divers were clearing fishing nets from its propellers, he said.

The Chinese ship then emitted dangerous sonar pulses, the minister added.

This had posed "a risk to the safety of the Australian divers, who were forced to exit the water", Defence Minister Richard Marles said in a statement on Saturday.

The divers suffered minor injuries that were likely caused by the sonar, Mr Marles said.

"Australia expects all countries, including China, to operate their militaries in a professional and safe manner," he said.

The Australian long-range frigate HMAS Toowoomba had communicated its intention to conduct diving operations on normal maritime channels, and using internationally recognised signals, the statement said.

There has been no comment for the Chinese government.

According to the Diving Medical Advisory Committee, a London-based body, high levels of underwater sound can cause "dizziness, hearing damage or other injuries" to divers.

The reported incident occurred on Tuesday in Japan's Exclusive Economic Zone. HMAS Toowoomba was conducting operations in support of UN sanctions enforcement, Mr Marles said, without giving details.

Earlier this month Australian Prime Minister Anthony Albanese made a breakthrough trip to China, and hailed "significant progress" in relations between the Pacific powers.

However tensions remain, notably over security. Australian has expressed concern over China's growing assertiveness in the Asia-Pacific region.

Canberra has recently deepened military ties with the US and overhauled its defence posture in a bid to counter potential threats from China.