Japan has lodged a formal diplomatic protest with China over Chinese Coast Guard vessels sailing into waters close to a disputed island in the East China Sea.

Japan's embassy in Beijing on Sunday expressed its concern over the incident. The embassy also lodged a formal diplomatic protest with the Chinese foreign ministry saying that the Senkaku group of islands in the East China Sea are "an inherent territory of Japan," reported AFP news agency.

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A Japanese Coast Guard patrol ship reportedly detected four China Coast Guard ships as they entered the contested waters close to disputed Senkaku Island at 10 a.m. local time on Sunday, the Japanese Coast Guard said in a statement. The patrol ship also issued warnings to the Chinese vessels and asked them to leave the contested waters immediately.

"A Japanese coast guard patrol ship communicated warnings to the Chinese ships, saying that they must leave the waters. The ships left roughly two hours later," the statement said.

China and Japan have long been engaged in a bitter territorial dispute in the East China Sea. Bejing is claiming ownership of the Japanese-controlled Senkaku group of islands, which is known as Diaoyu in China. China is also engaged in another territorial dispute with the Philippines and Vietnam in the South China Sea, also known as West Philippines Sea.

In July, an international arbitration tribunal ruled for the Philippines and rejected Beijing's claims of historic ownership over territories in the South China Sea. 

Tagschina, Japan, East China Sea, Senkaku Islands, Chinese Coast Guard