Chinese fighter jets approached abnormally close to two Self-Defence Forces planes over international waters in the central part of the East China Sea, according to the Defence Ministry.
One of the Chinese fighters flew as close as 30 meters to one of the SDF planes, the ministry said Saturday.
According to the ministry, the close encounter occurred in an area where Japan's air defence identification zone (ADIZ) and China's ADIZ, which Beijing recently claimed, overlap.
"It was an extremely unusual situation for military aircraft of Japan and China to come so close to a collision," a ministry official said.
According to the announcement, at about 11 a.m. Saturday, two Chinese Sukhoi Su-27 fighters approached a Maritime Self-Defence Force OP-3C reconnaissance aircraft from behind. The Japanese aircraft was gathering images.
One of the two Chinese fighters crossed the MSDF plane's wake from a distance of about 50 meters.
About an hour later, two Su-27 Chinese fighters approached an Air Self-Defence Force YS-11EB aircraft, which was also gathering information. The ministry said one of the Chinese fighters approached about 30 meters from the ASDF plane.
The SDF planes were on information-gathering missions. China and Russia are conducting joint military exercises in the East China Sea.
Defence Minister Itsunori Onodera said late Saturday the government demanded China prevent a recurrence of similar incidents.
In November last year, China unilaterally announced that it had set up the ADIZ in airspace that includes the skies over the Senkaku Islands in Okinawa Prefecture. The Japanese government protested the move.