The Maritime Self-Defense Force and the U.S. Navy are jointly operating an undersea submarine detection system on the floor of the Pacific side of the Nansei Island chain, including Okinawa, as part of efforts to counter China's rising maritime activities, sources said.

The latest model of the sound surveillance system, or SOSUS, allows Tokyo and Washington to detect Chinese submarines traveling from the East China Sea and Yellow Sea to the Pacific, sources in the Defense Ministry and the MSDF said Wednesday.

It is the first time that the existence of a listening system solely targeting China has been revealed.