Japan's Defense Minister Itsunori Onodera has termed the flybys by Chinese fighter aircraft as "an extremely dangerous action" against Japanese aircraft engaged in normal reconnaissance operations over international waters.
"We have lodged a stern protest to the Chinese side, via diplomatic channels," he said.
On Wednesday, in two separate episodes, Chinese Su-27 fighters flew dangerously close to two Japanese propeller-driven reconnaissance airplanes in skies over the East China Sea, the New York Times quoted Japan's Defense Ministry, as saying in a statement. imilar flybys in the same area took place several weeks ago.
The flybys are the latest escalation in an increasingly tense test of wills between China and Japan for dominance of the East China Sea, which includes a group of uninhabited islets that both nations claim.
A similar encounter took place late last month, when Chinese fighter planes flew as close as 100 feet to Japanese reconnaissance planes in the same area.
Japan's Defense Ministry said the incidents had taken place in airspace where both nations claim overlapping "air defense identification zones".
Chinese officials refused to comment.