Japan scrambled fighter jets from nearby Okinawa after a Chinese state aircraft flew over the territorial airspace of the islands, which China calls the Diaoyu. Japan’s defence ministry said the incident was the first violation of Japanese airspace by a Chinese official aircraft since at least 1958.
"It is extremely deplorable," said Osamu Fujimura, Japan’s chief government spokesman.
The incident will raise tensions in a diplomatic dispute that has already this year chilled ties between Tokyo and Beijing to their worst level in decades.
Beijing, which says Japan stole the islands in the late 19th century, has in recent months dramatically stepped up its challenges to Japan’s effective control of the waters surrounding the Senkaku.
The Chinese foreign ministry on Thursday said the Chinese aerial surveillance of the Diaoyu was "completely normal" and that Japan should stop entering the islands’ waters and airspace.
The China Maritime Surveillance aircraft’s flight over the Senkaku on Thursday is likely to fuel calls within Japan for stronger action to prevent such incursions and to assert sovereignty over the islands. The territorial dispute is already one of the top foreign policy campaign issues ahead of Japan’s general election on Sunday, a vote that is likely to result in a markedly more nationalist tone to foreign policy.
Shinzo Abe, leader of the opposition Liberal Democratic Party (LDP) and favourite to become prime minister, has stressed the need for a more robust defence of the Senkaku. He has promised increased spending on Japan’s coast guard and defence forces, saying more material resources are essential to block Chinese incursions.
The LDP has also pledged to consider stationing Japanese government officials on the islands, a move that would be considered hugely provocative by Beijing. Chinese officials say their increasingly assertive challenges to Japanese control of the islands are a response to what they call the Japanese government’s illegal purchase of three of the islands from their private owner. Japanese officials say the government bought the islands, which it already rented, in order to preserve the status quo by blocking an effort by the then right-wing Tokyo governor to buy them for development.
The Japanese air force scrambled eight F-15 fighters and an airborne early warning aircraft in response to the Chinese flight, the defence ministry said.
But NHK, the Japanese state broadcaster, reported that the Chinese aircraft had left the territorial airspace by the time the Japanese aircraft arrived on the scene.
The Japanese defence ministry released a photograph taken by the Japanese coast guard of the Chinese aircraft that showed it to be a small two-engined turboprop aircraft with official markings. China’s State Oceanic Administration said an aircraft had accompanied four vessels on a patrol that began on Thursday. The group contacted Japanese ships in the area and "ordered them to leave territorial waters immediately", a statement on the website of the Oceanic Administration said.
Zhou Yongsheng, a foreign policy expert at China Foreign Affairs University, said the exercise was meant to "demonstrate China’s jurisdiction over Diaoyu".
Mr Zhou said China would "normalise this kind of flight since we already announced our territorial baseline". But he added the maritime surveillance department would not be able to send aircraft regularly as they have only four.