Japan protested to Beijing on Sunday after a few Chinese coast guard ships were seen sailing into the territorial waters surrounding disputed islands in the East China Sea.

According to the Japan Coast Guard, four Chinese vessels entered the waters surrounding islets of Senkaku in Japan and the Diaoyu in China, around 10 am local time. It said the vessels left the disputed waters within an hour.

The director-general of the Japanese foreign ministry's Asian and Oceanian affairs bureau, Kenji Kanasugi issued a protest to the Chinese embassy in Tokyo to look into the matter. The ministry said in a statement that the Chinese ships' "incursion" violated Japan's sovereignty.

"Despite Japan's repeated strong protests, China has continued to take unilateral actions that raise tensions on the ground, and that is absolutely unacceptable," the statement said.

Recently, the conflict between Japan and China has been rising due to "China's incursions into the waters of the Tokyo-controlled disputed islands". Since Aug 5, Japan has lodged at least 32 protests regarding 30 intrusions by Chinese vessels in the territorial waters.

Apart from this, both the nations are also having disputes regarding the South China Sea territorial claims.