Prime Minister Shinzo Abe told Japanese troops on Sunday that Japan would not tolerate the use of force to change the region's status quo, comments likely to rile Beijing which is locked in a long and bitter territorial dispute with Tokyo.
"Use of force for changing the status quo" is an expression often used by Japanese politicians and security experts to indirectly refer to what they see as China's aggressive maritime expansion in the East China Sea and the South China Sea.
Abe's comments are the second in as many days in which he has effectively said Japan is ready to be more assertive towards China. They came as China military aircraft flew near Japan for a third day in a row, prompting Tokyo to scramble fighter jets each time.
Abe is seen as a hawkish nationalist who wishes to revise a post-war pacifist constitution drafted by the United States and strengthen Japan's defence posture.
His comment on Sunday, made at an annual troops review, comes after the Chinese Defence Ministry warned Japan not to underestimate China's resolve to take whatever measures necessary to protect itself.
"Development of weapons of mass destruction and ballistic missiles by North Korea. Provocation against our sovereignty. The security environment surrounding Japan is getting tougher," Abe told the military review, which consisted of some 3,900 troops, 240 vehicles and 50 aircraft.
"In order to show our firm national intention that changing the status quo by force will not be tolerated, we need to carry out various activities such as surveillance and information gathering."
Ties between Asia's two largest economies deteriorated sharply after Japan bought three of the disputed East China Sea islets, called the Senkaku in Japan and Diaoyu in China, from a private owner in September 2012, sparking large protests and boycotts of Japanese goods across China.
Patrol ships from both countries have been shadowing each other near the islets, raising fears that an accidental collision or other unintended incident could develop into a larger clash.
Abe said Japanese troops should discard the notion that all they should do in peace time was train, calling on them to contribute to peace and stability.
"It is your responsibility to resolutely defend the people's lives and property as well as our territory, waters and airspace, and to contribute to the world's peace and stability," Abe said.
"I need you to discard such old notions that all you need to do in a peace time is training, and that defence forces can be a deterrent just by existing."
In the latest sign of tensions between the region's two heavyweights, Japan on Sunday scrambled fighter jets after two Chinese bombers and two airborne early warning planes flew near Japan's southern islands into the Pacific and then back into the East China Sea. No violation of Japanese airspace took place.
The same formation of Chinese aircraft made similar flights on Friday and Saturday.
A Japanese Defence Ministry spokesman said it was quite rare for Chinese planes to fly close enough to Japan to trigger Japanese scrambles for three days in a row while maintaining the same formation and taking the same route.