China has declared its first-ever air defence zone covering the East China Sea, in a move expected to escalate long simmering tensions with Japan, possibly even raising the chance of conflict on - and over - the high seas.
In response, Tokyo has lodged a "strong protest" over the zone's establishment.
The new zone overlaps with a similar zone that Japan has; it covers a wide area of the East China Sea between South Korea and Taiwan that includes the Tokyo-controlled islands known as Senkaku to Tokyo, but claimed and known as Diaoyu by Beijing.
Beijing also issued a set of rules for the zone, known as the East China Sea Air Defence Identification Zone, saying it will adopt "defensive emergency measures" on aircraft that defy its rules, although it did not elaborate further.
The Defence Ministry said on Saturday morning, as it announced the establishment of the zone which kicked in with immediate effect, that this was a "necessary measure" as China exercises its right to self-defence.
"It is not directed against any specific country or target," spokesman Yang Yujun added on the ministry's website.
China will establish similar zones "at the right moment after necessary preparations", he said.
Mr Junichi Ihara, who heads the Japanese Foreign Ministry's Asian and Oceanian affairs bureau, made a protest by phone to Mr Han Zhiqiang, minister at the Chinese Embassy in Japan, the ministry said in a statement. Japan could "never accept the zone" as it includes the Tokyo-controlled Senkaku islands, the statement said.
Experts say the zone is likely to sour Sino-Japan ties further even as a Japanese business delegation visited Beijing last week, hoping to mend ties between the two sides in the light of the tense political climate.
But the Chinese position could be a reaction to recent talk of Tokyo's plans to shoot down drones that invade Japanese airspace, they said, and an attempt to prevent its military activities near the disputed islands from being blocked.
Mr Wendell Minnick, Asia bureau chief of the weekly defence paper Defence News, told The Sunday Times that China tends to "push the envelope" and then gauge the reaction in the hope of gaining more ground.
But this move might anger not only Japan. Its ally the United States will also be closely watching how Beijing attempts to enforce this zone, he said.
Professor Li Mingjiang of the S. Rajaratnam School of International Studies said while Beijing will not blatantly challenge Japan's airspace, it could "test the waters" and send its own fighter jets and drones near the disputed islands.
"Mutual suspicion and distrust will increase to some extent. The next step is to see how China and Japan establish a modus operandi to avoid accidents or miscalculations," he added.
Already, the Chinese air force conducted its first patrol inside the zone yesterday, the ministry said in a separate statement.
Shanghai-based security analyst Ni Lexiong told The Sunday Times that the South China Sea, where Beijing has maritime disputes with ASEAN countries like the Philippines and Vietnam, could be next in line.
But Mr Minnick thinks such a zone will be harder to enforce as the South China Sea encompasses a much larger area. Similarly, Prof Li thinks this is unlikely as China is not challenged in the airspace over the area and has been taking a more moderate tone in settling disputes there.
"The Taiwan Strait could be a more likely candidate for a similar zone," he added.
But the timing of the announcement could also be related to the recent Communist Party Third Plenum, a key policy summit held earlier this month where plans to form a national security commission to better coordinate security issues were announced.
"China has been taking steps to further develop its security with both domestic and international measures, so this could be the latest measure to build up its national defence," Professor Ni said.
Along with the zone's creation, the ministry released a set of identification rules that must be kept by all planes entering the area. Aircraft, for instance, must maintain two-way radio communication.
Spokesman Mr Yang noted that more than 20 countries have established similar air defence zones since the 1950s.
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