BEIJING, Dec. 30 -- Activity in China's Air Defense Identification Zone (ADIZ) has not been disturbed since the ADIZ was established a year ago, said an air force spokesman on Tuesday.

Shen Jinke, a spokesperson of China's Air Force, said the ADIZ over the East China Sea has a defensive act to safeguard the nation and to maintain aviation order.

The Air Force controlled the ADIZ through regular patrols, said Shen, adding that the Air Force would remain on high alert.

Staff on duty have been swift in identifying foreign military aircraft entering the ADIZ, and putting them under surveillance till they leave.

When abnormality or unspecified circumstances occurred, the air force took action appropriate to the level of threat, Shen said.