South Korea scrambled Air Force jets Wednesday to counter a Chinese military plane flying in the country's air defense domain without notice, defense authorities in Seoul said.

It entered the Korea air defense identification zone (KADIZ) at around 7:37 a.m. and moved over southern and eastern waters for about four hours, according to the Joint Chiefs of Staff (JCS).

"(We) took normal tactical measures," such as sending a warning message and dispatching Air Force jets to track and monitor it, the JCS added.

More than 10 aircraft, including F-15K fighter jets, were mobilized, a source said later.

It marked the second flight of a Chinese aircraft, believed to be for military reconnaissance, in the KADIZ in a month.

There were similar incidents in January, February and April as well.

An air defense identification zone is airspace over land or water declared by a state for the early identification and location of foreign planes approaching its territory. It's not defined in any international law or treaty.

The KADIZ near Ieo Island, a Seoul-controlled submerged rock south of Jeju Island, overlaps with the air defense zones designated by China and Japan, a source of potential tension among the regional powers. (Yonhap)