China has in recent months ramped up its long-range air force drills, particularly around Taiwan, claimed by China as its own.
The air force said in a statement that fighter and bomber aircraft flew through the Tsushima Strait that separates South Korea from Japan and into international waters in the Sea of Japan.
The Sea of Japan is not Japan's, and the drills were lawful and reasonable, air force spokesman Shen Jinke said in the statement, describing the exercises as routine and pre-planned.
In Seoul, South Korea's Joint Chiefs of Staff said five Chinese military planes were spotted entering the Korean Air Defence Identification Zone, and fighter jets scrambled in response.
The Chinese aircraft also flew through Japan's air defence identification zone, it added.
"Our fighter planes took normal tactical measures, identifying the models of the Chinese planes and flying aerial surveillance until they left," the South Korean statement said.
Chinese air force spokesman Shen alluded to the scrambled aircraft, saying they "responded to interference from foreign military aircraft" but were able to achieve the aim of their drill.
There was no immediate reaction from the Japanese government.
Taiwan monitored Japan sending F-15 fighters to intercept, Taiwan's defence ministry added in its statement.
China's air force last week conducted "island encirclement patrols" near Taiwan, after a senior Chinese diplomat threatened that China would invade the self-ruled island if any U.S. warships made port visits there.
China suspects Taiwan President Tsai Ing-wen, who leads the independence-leaning Democratic Progressive Party, wants to declare the island's formal independence. Tsai says she wants to maintain peace with China but will defend Taiwan's security.
China's air force exercises also come amid regional tensions over North Korea's nuclear and missile programmes, with bellicose rhetoric from both North Korea and U.S. President Donald Trump.
(Reporting by Ben Blanchard; Editing by Nick Macfie; Additional reporting by Hyonhee Shin in Seoul, Linda Sieg in Toyko and Jess Macy Yu in Taipei)
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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