China's military sent several fighter jets and an early warning aircraft on patrol into disputed air space over the East China Sea on Thursday, the Chinese state news agency Xinhua reported, quoting a spokesman for the People's Liberation Army Air Force.
The move raises the stakes in a standoff with the United States, Japan and South Korea over the zone. Japan and South Korea sent their own military aircraft through the air space on Thursday.
(Read more: US cautions airlines flying over East China Sea)
The Chinese patrol mission was "a defensive measure and in line with international common practices," said Shen Jinke, a spokesman for China's air force, in the Xinhua article.
Ties between China and Japan have been strained for months by the dispute over the islands in the East China Sea, called the Diaoyu by China and the Senkaku by Japan. The islands are currently under Japanese administrative control.
China last week unilaterally announced that foreign aircraft - including passenger aircraft - passing over the islands would have to identify themselves to China.
Earlier this week, Washington sent two unarmed B-52 bombers through the airspace without first informing Beijing, a sign of support for its ally Japan.
Although there are risks of a confrontation in the defense zone, U.S. and Chinese military officials have stepped up communication with each other in recent years and are in regular contact to avoid accidental clashes breaking out.
U.S. Vice President Joe Biden is visiting China, Japan and South Korea next week, and will try to diffuse tensions over the issue, senior U.S. administration officials said.
U.S. officials did not immediately respond to requests for comment on Thursday's Chinese flight, which Xinhua described as "normal air patrols" in the new air defense zone Beijing has declared.
(Read more: US, Japan slam China airspace rules on islands)
The article 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."