Tokyo has lodged an official protest with Beijing after Chinese ships entered the territorial waters of disputed islands in the East China Sea, Japan's NHK TV reported on Wednesday.
Four Chinese maritime surveillance ships were observed near the territorial waters of the Japanese held islands, known as the Senkakus in Japan and the Diaoyus in China, on Wednesday at about 8:30 a.m. local time [23:30 GMT].
At 12:30 p.m. [3:30 GMT], three of the ships ignored warnings from Japanese patrol vessels and crossed into the territorial waters.
“The Senkakus are Japanese territory and entering Japan’s territorial waters is unacceptable,” the head of Asian Affairs at the Japanese Foreign Ministry, Shinsuke Sugiyama, said during a telephone conversation with a Chinese embassy official. “We demand the ships leave [Japan's] territorial waters.”
It is the second time in the last two days Chinese surveillance ships have entered the territorial waters around the islands. On Tuesday four Chinese ships entered the waters around the islands and remained there about four hours.
Relations between the two countries have plummeted to their lowest level in years over their competing claims to the islands.
The dispute has triggered violent anti-Japanese protests across China and caused Japanese companies to suspend operations in China.
The tensions escalated in August after Japan formally announced its decision to buy three of the five disputed islands from the Kurihara family for 2.05 billion yen ($26.1 million).
The islands, which are also claimed by Taiwan, potentially contain large reserves of hydrocarbons.
Japan claims it has occupied the islands since 1895, while China maintains the islands were recognized as Chinese as early as 1783.