As relations with China continue to deteriorate, Japan is embarking on its biggest military buildup in at least four decades.

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

Japan's Defense Minister Koizumi Shinjiro has again expressed concern over Chinese military aircraft directing radar at Japanese Air Self-Defense Force fighter jets over international waters off Okinawa's main island in southern Japan on Saturday.

China and Japan ties, already frayed by comments made by Prime Minister Sanae Takaichi on Taiwan, came under further strain at the weekend after a Chinese fighter aircraft trained fire-control radar on Japanese military jets for the first time.

The buildup comes as Beijing steps up pressure on Prime Minister Sanae Takaichi over her recent remarks suggesting Japan might intervene militarily if China were to attempt to seize Taiwan

The Japanese government is taking uncomfortable steps to prepare its citizens for a possible future war that its military would not be able to avoid.

China’s Liaoning carrier conducts air drills near Japan, heightening tensions as both nations trade diplomatic accusations over military actions.

Over the weekend, China and Japan came dangerously close to a mid-air military conflict. Japan says Chinese fighter jets from the aircraft carrier Liaoning locked fire-control radar on Japanese warplanes — an aggressive move just one step short of missile launch.