Chinese Foreign Ministry spokesperson Lu Kang made the remarks at a daily press briefing.
Lu said that two ships of Japan's maritime self-defense force had earlier Thursday entered the Contiguous Zone of Chiwei Islet, which belongs to China's Diaoyu Islands. The ships have since left the area after tracking and surveillance by the Chinese navy.
"Diaoyu Island and its affiliated islands have always been an inherent part of Chinese territory," said Lu. "Japan's relevant actions cannot change the fact that Diaoyu Islands belong to China and cannot shake China's determination to safeguard its territorial sovereignty."
China urges Japan to take concrete measures to improve bilateral ties, and meet China half-way in line with the four-point principled consensus reached in 2014, he said.