Japan's Defense Ministry says it confirmed that five Chinese naval ships sailed around the entire Japanese archipelago.
The ministry spotted three vessels on Tuesday, including guided-missile destroyers, sailing in waters about 60 kilometers southeast of Taisho Island, part of Senkaku Islands in the East China Sea. Japan controls the islands. The Japanese government maintains the islands are an inherent part of Japan's territory. China and Taiwan claim them.
The ministry said the vessels came to the area after passing through the contiguous zone between Yonaguni and Iriomote Islands in Japan's southwestern prefecture of Okinawa.
The ministry also found other two vessels, including a guided-missile destroyer, traveling in waters between Okinawa's main island and Miyakojima Island from the Pacific toward the East China Sea.
The ministry said the five ships then got together and sailed northwest in waters about 80 kilometers off Okinawa's Kumejima Island.
The ministry said the maneuver was conducted as if the ships were moving through the flanks of much of Sakishima Islands, an archipelago in Japan's southwest.
On April 30, the ships passed through the Tsushima Strait before entering the Sea of Japan from the East China Sea. The fleet then crossed the Soya Strait between Japan's northernmost prefecture of Hokkaido and the Russian island of Sakhalin to reach the Pacific.
It then sailed southward in the ocean, having completed an apparent circle around the entire Japanese archipelago in about half a month.
The ministry said it is the first time it has confirmed that Chinese navy ships navigated through the flanks of Sakishima and that they circled all of the Japanese archipelago. It said it conveyed its concern to China via a diplomatic channel.
The ministry said the voyage is seen as an unprecedented expansion of China's military activity as the vessels chose routes of passage close to Japan's territory.