Japan deployed ground force units including missile squads Tuesday in two southwestern islands between the East China Sea and the western Pacific where Chinese naval vessels are actively sailing.

About 550 Ground Self-Defense Force members were stationed on Amami-Oshima Island in Kagoshima Prefecture, nearly 400 kilometers south of the southwestern main island of Kyushu. Some of them were assigned to the land-to-air and land-to-ship missile units, the Defense Ministry said.

The other was a 380-member security unit on Miyako Island in Okinawa Prefecture, around 300 km southwest of the main island of the prefecture. The number of its members will increase to 700 to 800 to introduce another missile unit in 2020 or later, the ministry said.

"Japan's defense front line is now the southwestern region, so we'll beef up our capability and deterrence in that area," Defense Minister Takeshi Iwaya told a press conference, adding that the new units can also "deal with disasters quickly."

The ministry is also preparing to deploy missile and security units with some 500 to 600 GSDF members on Okinawa's Ishigaki Island, about 100 km southwest of Miyako Island.

The moves come as Japan is aiming to fill what the ministry describes as a defense "vacuum" in the area. Previously, its forces were only stationed on Okinawa's main land and the country's westernmost island of Yonaguni, where a 160-member GSDF garrison was set up in 2016.

Miyako, Ishigaki and Yonaguni islands are near the Tokyo-controlled Senkaku Islands in the East China Sea, which Beijing claims, calling them Diaoyu. Chinese ships have repeatedly entered Japanese waters around the islands, keeping tensions high.

Also Tuesday, the GSDF increased the number of its Amphibious Rapid Deployment Brigade by 300 to about 2,400 in a bid to reinforce the ability to defend remote islands in southwestern Japan.

Dubbed the Japanese "Marines," the brigade was launched as the country's first full-fledged amphibious force in March last year, based in Kyushu's Nagasaki Prefecture.

Under the latest Medium Term Defense Program that covers a five-year period from April 1, Japan is planning on strengthening its defense system at the far-flung islands in the southwest.