Four Chinese warplanes entered the Korea Air Defence Identification Zone (KADIZ) followed by 15 Russian aircraft, according to South Korea's Joint Chiefs of Staff (JCS).
The South Korean military dispatched air force fighters to take tactical measures.
The South Korean military said in a statement the Chinese military had informed South Korea that its planes were carrying out routine training before the Chinese aircraft entered the KADIZ.
"This incident seems to be a joint military drill between China and Russia but it requires a further analysis," the JCS said in a statement.
In July last year, South Korean warplanes fired hundreds of warning shots toward Russian military aircraft on a joint air patrol with China, when they entered South Korean airspace.
South Korea and Japan, which both scrambled jets to intercept the patrol at the time, accused Russia and China of violating their airspace. Russia and China denied it.