China has expressed regret over the South Korean decision to expand its air defense identification zone (KADIZ), a foreign ministry spokesman said on Monday.

Spokesman Hong Lei made the remarks after South Korea on Sunday announced a southward expansion of the KADIZ, encompassing submerged rocks within the overlapping exclusive economic zones (EEZ) of South Korea and China.

Hong said China and South Korea have maintained communication over the establishment of China's ADIZ and the expansion of the South Korean air zone.

Both the Chinese foreign ministry and the defense ministry have stated their position to the South Korean government and demanded they cautiously and properly handle the issues, he said.

"China is ready to maintain communication with South Korea in line with the principle of equality and mutual respect," he said.

The South Korean Defense Ministry said its eastern and western boundaries remained the same as before, and that the new zone would take effect from December 15.

Japan's Chief Cabinet Secretary Yoshihide Suga on Monday said the expansion of the KADIZ won't be a problem as Seoul had informed Tokyo in advance about its plans.

"We don't think it's going to be a problem at the moment," Suga, the government's top spokesman, told reporters in Tokyo.

Xinhua - AFP