The nation's armed forces, called the Self-Defence Forces, launched a squadron of four E-2C early warning planes at its air base in Naha on the main Okinawan island today, the Jiji and Kyodo news agencies reported.
This is the first time such planes have been based on the island. At the inauguration ceremony in Naha, Defence Minister Itsunori Onodera said Japan faced a "dangerous situation" as China's continual attempts to "change the status quo by force and threaten the rule of law could trigger emergencies," Kyodo News reported.
Japan's air force possesses 13 E-2C airborne early warning planes at the Misawa base in northern Japan. Four of these have been transferred to the Naha base.
The number of personnel there will be doubled to about 130 by March 2015.
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Japan scrambled fighter jets against approaching Chinese aircraft 415 times in the year to March 2014, up from 306 times in the preceding year, Jiji said citing defence ministry statistics.
Yesterday, a ceremony was held to start building a radar surveillance unit on Yonaguni, Japan's westernmost island, despite protests from islanders fearing the unit will trigger attacks, the reports said.
Chinese ships and planes have approached the disputed island group, repeatedly moving into its territorial waters and airspace, after Tokyo nationalised some of the Senkakus in September 2012, to confront Japanese patrols.
Radar equipment will be installed at the ground force unit on Yonaguni to monitor ships and aircraft in the East China Sea, the reports said.
About 150 personnel will be deployed at the radar unit by the end of March 2016.