The Chinese reaction, issued by Foreign Ministry spokesman Hong Lei, came a day after the Japanese Defense Ministry expressed concern in its annual report about regional security, as China's naval activity in the Pacific becomes routine.
"China strongly opposes ... the groundless criticisms on China's normal national defense development and military activities, and the irresponsible remarks on China's internal affairs made by Japan's annual defense white paper," Hong said, the official Xinhua news agency reported.
Hong said China has made solemn representations to Japan on the issue, the report said.
The spokesman was quoted as saying Japan has drawn wide attention from regional and international communities, by making various excuses for its continuous arms expansion, reinforcement of military alliance and distorting facts on regional security issues in recent years.
"What is Japan's real motivation by doing so?" Hong asked, while urging Japan to give serious introspection to whether such actions could be conducive to the regional peace and stability, Xinhua said.
The Japanese Defense Ministry said China's Pacific activity indicated it could widen its maritime sphere and conduct operations and training as routine practices in waters near Japan, including the East China Sea, the Pacific Ocean and the South China Sea.
The report said Japan should pay attention to the activities of Chinese vessels in the East China Sea, where the Japanese-controlled Senkaku Islands are located. China calls them Diaoyu Islands.