The Defence Ministry announced that two Chinese Su-27 fighter jets flew abnormally close to Japanese Air Self-Defence Force and Maritime Self-Defence Force planes over the East China Sea.
The incidents took place Wednesday in an area where Japan's air defence identification zone and China's recently claimed ADIZ overlap.
Defence Minister Itsunori Onodera was quoted as telling visiting Australian Defence Minister David Johnston that Japan lodged a strong protest with China via diplomatic channels.
On May 24, two Chinese fighter jets approached unusually close to two SDF planes over international waters in the central part of the East China Sea.
On that occasion one of the Chinese fighter jets flew as close as 30 meters to one of the SDF planes.