The Chinese warplanes included two bombers, two fighter jets and a reconnaissance plane an official confirmed.
The jets were detected infringing on the Korean Air Defence Identification Zone (KADIZ), a disputed territory from the southwest of Ieo Island, at around 10am.
And according to Seoul’s chief of staff, they did not leave the zone until 1.47pm.
A statement said: ”Our military confirmed that they are military planes of China through the Air Force’s Master Control and Reporting Centre.”
South Korea’s fighters took “normal tactical measures” until the Chinese planes left, it said.
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Both Seoul’s F-15K and KF-16 fighters were mobilised for a possible contingency.
An official added: “We talked with the Chinese side over a hotline and it said the operation was part of a routine exercise.
“We are analysing its exact intention.”
The incident took place in an area where both South Korea and China have competing air space claims.
And it comes following last week’s state visit by President Moon Jae-in while tensions with North Korea continue to build.
Two US military B-1B Lancer strategic bombers based in Guam conducted drills in the KADIZ earlier this month as part of the Vigilant Ace drills with South Korea.
The bombers trained with more than 20 fighter jets in the exercise, which began on December 4.
The aircraft entered the disputed region over the waters south of Jeju Island and conducted simulated bombing drills over the Yellow Sea near North Korea and China.
A total of 12,000 US service members are taking part in the annual Vigilant Ace drills alongside South Korean troops.
The exercise has been condemned by North Korea, which said the drills prove that US President Donald Trump is “begging” for nuclear war.