Chinese state-run media on Monday played down South Korea's expansion of its air defence identification zone, weeks after Beijing provoked regional fury by establishing its own.

State-run media mostly reported Seoul's Sunday announcement without issuing commentaries, while the foreign and defence ministries did not immediately comment.

Seoul and Tokyo, along with Washington, which is in security alliances with them both, have all refused to accept Beijing's air defence identification zone (ADIZ).

The Chinese ADIZ overlaps with both Japan and South Korea's, which were set up decades ago, and includes territories disputed by both countries.

Beijing has lashed out at historic rival Tokyo, with which it is embroiled in a row over islands in the East China Sea that has escalated since last year.

With Seoul, by contrast, China has sought to cultivate friendly relations, and the Chinese-language edition of the Global Times, which normally strikes a nationalist tone, said in an editorial: "China will not make a big deal out of this right now."

Korea's move was "opportunistic" in light of the more serious standoff between Beijing and Tokyo, it said, but added that "China respects Korea's interests".

"Korea is a friendly and important partner in China's development. Hopefully Korea will fully respond to China's goodwill, not go over the line," it said.

No editorials on the subject appeared in other major outlets, including the ruling Communist Party paper, the People's Daily, or the state news agency Xinhua, while reports on the news were mild.

"Although it objectively overlaps with China's ADIZ, it's an action South Korea took to ensure its interests and the demands of its people," the Global Times English-language news report quoted foreign affairs expert Su Hao as saying.

The move was not hostile, it cited Su as saying, though another expert was quoted as calling it provocative.

The China Daily, citing naval expert Yin Zhuo, said "Beijing and Seoul know that neither China's announcement nor South Korea's expansion is an offensive measure".

The muted responses were in line with comments by foreign ministry spokesman Hong Lei last Friday when asked about South Korea's plans to expand its ADIZ.

"China is ready to stay in communication with the ROK based on the principle of equality and mutual respect," he said, according to the foreign ministry website, adding that the move "should comply with international laws and conventions".

China established its ADIZ in late November, requiring all aircraft within it to obey its instructions or risk unspecified "defensive emergency measures".

The US, Japan and South Korea accused China of unilaterally changing the status quo and flew military and paramilitary aircraft into the area in shows of defiance.

Analysts have said Beijing established the ADIZ to further assert its claim to the islands known as Diaoyu in China and Senkaku in Japan, which controls them.