China has sent warplanes to its newly-established Air Defense Identification Zone over the East China Sea, state-run Xinhua News Agency reported Friday, after the US, Japan and South Korea have flown military aircraft earlier this week. "The People's Liberation Army Air Force conducted its first air patrol in the zone on Thursday, Shi Jinke, spokesman for the force, was quoted as saying. "The patrol mission was carried out by several fighter jets and an early warning aircraft," Shi said, stressing that the mission was "a defensive measure and in line with international common practices." Shi said China's air force is "on high alert and will take measures to deal with diverse air threats to firmly protect the security of the country's airspace." On November 23, China unilaterally set up the defense zone over a large area of the East China Sea, obligating all aircraft passing the area to notify Chinese authorities of their flight plans and identify themselves. The zone partly overlaps those of Japan and South Korea, including airspace above the Japan-controlled Senkaku Islands, which are also claimed by China. In response, Japan, South Korea, Australia and the US expressed regret, and Washington flew a pair of B-52 bombers on Tuesday through the area. Japanese Chief Cabinet Secretary Yoshihide Suga said Thursday that Japan's Air Self-Defense Force aircraft has also flown within the zone recent days without complying with Beijing's new rules. South Korea's military also conducted a surveillance flight through the zone on Wednesday without informing the Chinese authorities, the Seoul-based Yonhap News Agency reported Thursday. The move was in a clear sign that Seoul will not recognize the Chinese new airspace claim that partly overlaps South Korea's own zone and the South Korean-controlled submerged rock of Ieodo Island, it said.