I think the Japanese Navy in response should sail right through so called Japanese territorial waters in the South China Sea in response to this:

The Chinese coast guard entered waters Japan claims as its territorial limit around the Senkaku Islands over the weekend, less than 10 days after Japan’s prime minister warned Tokyo would use military force if China attacked Taiwan. Four Chinese vessels crossed into the 12-mile zone east of the Senkakus around 10:15 a.m. Sunday, according to a Japan coast guard statement released the same day. The uninhabited Senkakus — five islets and three rocky outcrops — lie about 105 miles east of Taiwan and 254 miles west of Okinawa. They are administered by Japan but also claimed by China and Taiwan.
You can read more at the link.




