SEOUL, Nov 30 (Reuters) - South Korea's military said it scrambled fighter jets as two Chinese and six Russian warplanes entered its air defence zone on Wednesday.The two Chinese H-6 bombers repeatedly entered and left the Korea Air Defence Identification Zone (KADIZ) off South Korea's southern and northeast coasts starting at around 5:50 a.m. (2050 GMT Tuesday), Seoul's Joint Chiefs of Staff (JCS) said.They re-entered the zone hours later from the Sea of Japan, known in South Korea as the East Sea, together with the Russian warplanes, including TU-95 bombers and SU-35 fighter jets, and left after 18 minutes in the KADIZ, the JCS said.Unlike a country's airspace - the air above its territory and territorial waters - there are no international rules governing air defence zones.In August, the JCS reported Russian warplanes entering the KADIZ, three months after Chinese and Russian aircraft made an incursion in May that was the first after South Korean President Yoon Suk-yeol took office."