Japan scrambled fighter jets on Wednesday after a Chinese military aircraft flew for the first time through international airspace near its southern islands out over the Pacific, in a move seen by Japan as underlining China's maritime expansion.
Ties between China and Japan have been strained by a territorial dispute over uninhabited East China Sea islets and hawkish Japanese Prime Minister Shinzo Abe won a decisive victory in upper house elections on Sunday.
Japan's Defense Ministry said a Chinese Y-8 airborne early warning plane flew through airspace between Okinawa prefecture's main island and the smaller Miyako island in southern Japan out over the Pacific at around noon and later took the same route back over the East China Sea.
"I believe this indicates China's move toward further maritime expansion," Japanese Defense Minister Itsunori Onodera told reporters, in comments carried on public broadcaster NHK.
Chinese government spokesmen were not immediately available for comment.
The waters around the disputed islands, called the Senkaku in Japan and Diaoyu in China, and which are to the west of Okinawa's main island, are rich fishing grounds and the sea floor around them could hold big oil and gas reserves.
Tension between China and Japan escalated last September when Japan bought three of the disputed islands from a private Japanese owner.
Since then, patrol ships and aircraft from both countries have been shadowing each other in the sea and skies around the islets.
That has raised fears of an unintended collision leading to a broader clash.
Abe has pledged to take a firm stance in the territorial dispute, but said in his news conference following the upper house election win that Japan's door was open to dialogue.