A Chinese fighter jet endangered an Australian military helicopter during an “unsafe” and “unacceptable” confrontation over the Yellow Sea, Australia said on Monday.

The Chinese air force J-10 jet dropped flares above and several hundred meters ahead of an Australian MH60R Seahawk helicopter which was on a routine flight on Saturday in the Yellow Sea as part of an operation to enforce sanctions against North Korea, Defence Minister Richard Marles said in a statement.

The helicopter, flying from destroyer HMAS Hobart, dodged the flares, but the possible impact would have been “significant”.

“This is a very serious incident, it was unsafe and it is completely unacceptable,” he said.

“We have formally expressed our concerns about this incident, and formally expressed that this was both unsafe and unprofessional.”

The confrontation put the aircraft and those on board at risk, although no one was hurt, the Department of Defence said in a separate statement.

This is the second such incident in six months to mar what has otherwise been a growing rapprochement between the two countries after years of strained relations and trade disputes.

Australia said in November a Chinese naval vessel injured some of its divers in Japanese waters using an underwater sonar. China denied it had used its sonar, however Australia rejected the explanation.

HMAS Hobart continues to operate in the area despite Saturday’s confrontation, Marles said. Australia has been participating in missions to enforce sanctions against North Korea in the region since 2018.

China’s Ministry of Defence did not immediately respond to a request for comment.