The Chinese ministry said in a statement that “China strongly urges Japan to immediately stop all action to undermine China's territorial sovereignty and return to a negotiated settlement to the dispute. If Japan insists on going its own way, it will bear all the serious consequences that follow.”
Japan and China have long been competing over the sovereignty of the islands, which would give the owner exclusive oil, mineral and fishing rights in surrounding waters.
China, however, does not recognize the ownership of the Japanese Kurihara family.
China has deployed two patrol ships to the disputed islands in the East China Sea immediately after the Japanese government announced it has purchased the islands from their private Japanese owner.
China's official Xinhua News Agency reported on Tuesday that two patrol ships of the China Marine Surveillance (CMS) have reached waters near the resource-rich islands to “assert the country's sovereignty.”
The move came after Japan's public broadcaster NHK announced that the sales contract to buy the three uninhabited islands, known as Senkaku in Japan and Diaoyu in China, from the private owner was signed on Tuesday morning.
China's Foreign Ministry on Monday warned that Beijing would not “sit back and watch its territorial sovereignty violated.”