A major and very dangerous incident occurred over waters off Japan's southern islands on Saturday, but has only been publicly revealed Sunday. Chinese PLA military aircraft locked radar on Japanese fighter jets, at a moment Japan-China relations have deteriorated to their worst in many years

Japan and Australia are urging calm in the wake of the aerial encounter, with contrasting accounts and accusations from each side that the other is acting dangerously. Defense Minister Shinjiro Koizumi said his country and allies have formally protested it, calling this "an extremely regrettable" act and "a dangerous" one which exceeds "the scope necessary for safe aircraft operations."

"We have lodged a strong protest with the Chinese side and demanded strict preventive measures," Koizumi said.

According to a description of the event from Tokyo's side:

Japan’s Defense Ministry said China’s military aircraft J-15 took off from the Chinese carrier Liaoning near the southern island of Okinawa on Saturday and "intermittently" latched its radar on Japanese F-15 fighter jets on two occasions Saturday, for about three minutes in the late afternoon and for about 30 minutes in the evening. It was not made clear whether the radar lock incident involved the same Chinese J-15 both times.

Japan had scrambled its own jets apparently to monitor Chinese military flight actions in the region, and as readiness in case some kind of deeper intervention was needed:

Japanese fighter jets had been scrambled to pursue Chinese ones that were conducting aircraft takeoff and landing exercises in the Pacific. They were pursuing the Chinese aircraft at a safe distance and did not take actions that could be interpreted as provocation, Kyodo News agency said, quoting defense officials, when the radar lock happened. There was no breach of Japanese airspace, and no injury or damage was reported from the incident.

As for the Chinese side, its military responded in a statement alleging the Japanese aircraft of "harassment" during routine PLA exercises.

PLA Navy spokesman, Senior Colonel Wang Xuemeng, asserted, "We solemnly asked the Japanese side to immediately stop slandering and smearing, and strictly restrain its frontline actions. The Chinese Navy will take necessary measures in accordance with the law to resolutely safeguard its own security and legitimate rights and interests."

More from the Chinese version of events on the highly dangerous weekend encounter, which could have led to a full-blown shooting conflict:

Japanese Prime Minister Sanae Takaichi has slammed the radar lock-in as "extremely disappointing" and declared "We will act calmly and resolutely."

Takaichi herself has taken center stage in the weekslong controversy, which started when she made comments in a parliamentary meeting last month which made clear Japan could possibly intervene militarily in the scenario of China invading Taiwan. China has been retaliating through measures related to curbing trade, cultural exchanges, and tourism - coupled with threats of more punitive action to come.

Beijing has warned that Takaichi's verbalized stance constitute fighting words...

Lately, Chinese and Japanese vessels have also had tense encounters near disputed Japanese-owned islands, and each's coast guard ships have been involved in warnings and threats.