Japan began its first military expansion at the western end of its island chain in more than 40 years yesterday, breaking ground on a radar station on a tropical island off Taiwan.
The move risks angering Beijing, which is locked in a dispute with Tokyo over the nearby Diaoyu Islands - known as the Senkakus in Japan - which they both claim.
Japanese Defence Minister Itsunori Onodera, who attended a ceremony on Yonaguni island to mark the start of construction, suggested the military presence could be enlarged to other islands in the seas southwest of Japan's main islands.
"This is the first deployment since the US returned Okinawa [in 1972] and calls for us to be more on guard are growing," Onodera said. "I want to build an operation able to properly defend islands that are part of Japan's territory."
The military radar station on Yonaguni, part of a longstanding plan to improve defence and surveillance, gives Japan a lookout just 150 kilometres from the Japanese-held Diaoyu Islands.
Building the base could extend Japanese monitoring to the Chinese mainland and track Chinese ships and aircraft circling the islands.
Prime Minister Shinzo Abe's decision to put troops on Yonaguni shows Japan's concerns about the vulnerability of its thousands of islands and the perceived threat from China. The new base "should give Japan the ability to expand surveillance to near the Chinese mainland", said Heigo Sato, a professor at Takushoku University and a former researcher at the defence ministry's National Institute for Defence Studies.
"It will allow early warning of missiles and supplement the monitoring of Chinese military movements."
Japan does not specify an exact enemy when discussing its defence strategy, but it makes no secret of the fact that it perceives China generally as a threat as it becomes an Asian power that could one day rival Japan's ally in the region, the United States.
Japan, in its National Defence Programme Guidelines issued in December, expressed "great concern" over China's military buildup and "attempts to change the status quo by coercion".
China's decision last year to establish an air-defence identification zone in the East China Sea, including the skies above the disputed Diaoyu Islands, further rattled Tokyo.