BEIJING- China sent fighter jets and an early warning aircraft into its newly declared air defence zone, state media said on Friday, as Japan and South Korea stated they had defied the zone with military overflights.
The Chinese planes had conducted normal air patrols on Thursday as "a defensive measure and in line with international common practices," said Shen Jinke, spokesman for the People's Liberation Army (PLA) Air Force, according to state news agency Xinhua.
Mr Shen said China's air force would remain on high alert and take measures to protect the security of the country's airspace, Xinhua reported.
Japan and South Korea said on Thursday they had defied the air defence identification zone (ADIZ) declared by Beijing last weekend, showing a united front after US B-52 bombers did the same.
Chinese authorities are coming under domestic pressure to toughen their response to incursions into the zone that includes disputed islands claimed by China, which knows them as the Diaoyus, but controlled by Japan, which calls them the Senkakus.
The move triggered US and Japanese accusations of provocation as global concerns grew.
China's ADIZ requires aircraft to provide their flight plan, declare their nationality and maintain two-way radio communication - or face "defensive emergency measures".
But Tokyo said its coast guard and air force had flown unopposed in the zone without complying with Beijing's rules.