South Korean forces scrambled fighter jets to escort three Chinese military planes after they entered an overlapping air defence zone. The Chinese aircraft are reported to have flown into the airspace on Thursday, 18 August near South Korea's island of Jeju without alerting authorities in Seoul.

Beijing's aircraft, which included a bomber, quickly left the airspace after South Korean authorities issued a warning and dispatched the fighter jets, a military source told South Korea's Yonhap news agency.

The aerial incident has occurred amid tensions between the two countries over the deployment of the sophisticated missile defence system Terminal High Altitude Area Defense (Thaad) in the Korean peninsula. Washington and Seoul have agreed to position the missile-interceptor unit in South Korea in order to counter threats from North Korea, but both China and Russia have opposed the move saying their territories would also fall under Thaad's radar.

China's latest action of sending military jets is seen as more of a muscle-flexing exercise to show its displeasure over the proposed deployment. This was not the first time Beijing flew jets over the contested region. Earlier in 2013, China dispatched several warplanes and aircraft to the area.

South Korea scrambles jets against China
Chinese jets left the disputed air defence zone after a warning from South Korean forces Jason Lee/Reuters

Chinese planes entered the airspace in January 2016 as well but Seoul did not scramble fighter jets then.

The so-called air defence zone in the East China Sea itself has become a matter of territorial dispute between China and South Korea. In December 2013, Beijing unilaterally declared the zone infuriating both Seoul and Japan. In response, Seoul expanded its own zone, which includes a contested submerged rock and a key ocean research station, Leodo, on a reef.