China's air force is on "high alert" and has sent patrols into its new air defence identification zone in the East China Sea, the Defence Ministry said on Friday. China will remain on "high alert" and will take measures to "deal with diverse air threats" in its air space, People's Liberation Army spokesman Shen Jianke said in a statement posted on the ministry's website. The air force sent a patrol of fighter jets and an early warning aircraft on Thursday, dpa quoted Shen as saying. An earlier report by the ministry said China began patrols on Saturday, the day it declared the zone. The patrols were "a defensive measure and in line with international common practice," Shen was quoted as saying.