Japan and Australia have urged calm after Chinese military aircraft locked radar onto Japanese fighter jets, a month after the Japanese leader’s recent remarks on Taiwan that stirred tensions between Tokyo and Beijing.

Defence Minister Shinjiro Koizumi said Japan formally protested the incident, calling it “an extremely regrettable” act and a “dangerous” one that “exceeded the scope necessary for safe aircraft operations”.

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

Japan’s Defence 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 on 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.

The Japanese fighter jets had been scrambled to pursue Chinese jets that were conducting aircraft take-off and landing exercises in the Pacific. 

Japan's Defense Minister Shinjiro Koizumi, center, speaks to the media

Shinjiro Koizumi said Japan formally protested the incident in which a Chinese military aircraft locked its radar onto Japanese jets.  (AP: Kyodo News )

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 defence officials, when the radar lock happened. 

There was no breach of Japanese airspace, and no injury or damage was reported from the incident.

Senior Colonel Wang Xuemeng, spokesperson for the Chinese Navy, defended China’s flight training near the Miyako Island on Saturday, saying Beijing had announced the exercises beforehand and accused Japanese aircraft of “harassment.”

“We solemnly asked the Japanese side to immediately stop slandering and smearing, and strictly restrain its frontline actions,” Colonel Wang said in a statement posted Sunday on the Chinese Ministry of Defence website.

“The Chinese Navy will take necessary measures in accordance with the law to resolutely safeguard its own security and legitimate rights and interests.”

Relations between Japan and China have worsened after Japan’s Prime Minister Sanae Takaichi said in early November that its military could get involved if China were to take action against Taiwan, the self-governing island that Beijing claims as its own.

Australia and Japan, whose defence ministers held their scheduled talks in Tokyo on Sunday, expressed worry over the development.

Japanese Minister of Defense Shinjiro Koizumi, left, and Australian counterpart Richard Marles

Australia and Japan have agreed to bolster military ties to lead multilateral defence cooperation in the region. (AP: Eugene Hoshiko)

“We are deeply concerned by the actions of China in the last 24 hours,” Australian Defence Minister Richard Marles told a joint news conference Sunday after holding talks with Mr Koizumi. 

“We expect those interactions to be safe and professional.”

Australia does “not want to see any change to the status quo across the Taiwan Straits,” Mr Marles said, adding that China is his country’s largest trade partner and he wants to have productive relations with Beijing.

“We continue to advocate to China about these issues again, in a very calm, sensible and moderate way,” he said.

The two countries, during Sunday’s talks, agreed to bolster military ties to lead the region’s multilateral defence cooperation. 

The two ministers agreed to form a comprehensive “framework for strategic defence coordination” and discuss further details.

Tokyo has been accelerating its military build-up while expanding its defence ties beyond its only treaty ally, the United States. It now considers Australia to be a semi-ally.

Japan and China trade accusations after coast guard incident

Tokyo and Beijing have given different accounts of the clash as relations between the two countries continue to sour following comments made by Japan’s prime minister about Taiwan.

Mr Marles also visited a Mitsubishi Heavy Industries shipyard in Nagasaki on Saturday to observe production of the upgraded Mogami-class frigate that Australia chose in September as a replacement for its aging fleet.

Saturday’s radar lock is believed to be the first involving Japanese and Chinese military aircraft. In 2013, a Chinese warship targeted a radar onto a Japanese destroyer, Kyodo News reported.

Fighter jets use radars for search operations or fire control ahead of a missile launch.

Elsewhere in the Pacific, the Philippine coast guard said China fired three flares toward a fisheries bureau plane on patrol in the South China Sea on Saturday. 

Chinese forces fire flares to warn planes to move away from what they consider their airspace over the disputed waters.