A Chinese naval vessel enters the East China Sea en route to the Diaoyu Islands on Oct. 16, 2012. [Photo/Sina]

Chinese navy vessels' activities around the Diaoyu Islands [full coverage] are legitimate, the Ministry of Defense said on Tuesday.

Japan's Defense Ministry says it spotted early Tuesday seven Chinese naval vessels appear in waters 49 kilometers south-southeast of Yonaguni Island, Japan's westernmost inhabited island. The spotted Chinese warships included two destroyers.

"Chinese navy vessels' routine training and navigation in the waters in question is justified and legitimate," said the ministry's bureau for press affairs in a statement, condemning Japanese military aircraft's presence there.

"It should be pointed out that Japan in recent days sent military aircraft to the waters around the Diaoyu Islands, severely infringing on China's sovereignty and interests," said the statement, adding that China is now closely watching Japan's movement and demanding the Japanese to stop any actions that can complicate or magnify the issue.

China has kept sending fishery and surveillance ships to patrol the waters surrounding the Diaoyu Islands, since the "purchase" of China's Diaoyu Islands by the current Japanese administration.

Previously, China's five fishery patrol ships were sent to the waters off the Diaoyu Islands during the National Day holiday.

The island row has severely harmed the diplomatic ties between the two countries, brining the tension to a flashpoint.