MORE than 20 countries have set up air defence zones that require aircraft to obey self-identification rules, but China's move to join their ranks has unnerved its neighbours, especially Japan and its security ally, the United States.
There are good reasons to be concerned about China's first Air Defence Identification Zone (ADIZ) set up last Saturday over the East China Sea, say analysts.
One is location. The ADIZ overlaps Japan's zone, crucially over isles claimed by Beijing as Diaoyu and by Tokyo as Senkaku.
Bilateral ties sank to a 40-year low after Japan nationalised three of the Tokyo-controlled isles last year. In recent weeks, both sides threatened the use of military action after Chinese drones flew close to the contested area.
"The problem here is that the Chinese are being provocative in a region that is obviously contested and where tensions run high," said Singapore-based military expert Richard Bitzinger.
"Creating such an identification zone does not help reduce tensions or provide a way to reach a compromise or make the areas around the islands more stable."
Observers believe China's rules also appear more heavy-handed and menacing than those of zones enforced by other countries, including Japan, the US, Canada, Australia and Indonesia.
An ADIZ is an early warning concept that pre-defines an area outside a country's territorial airspace and monitors aircraft for security purposes. Such zones, their boundaries and rules are drawn up based on domestic laws.
"China is demanding that all aircraft comply with its newly issued regulations. In contrast, the US only requires planes heading directly to the US to comply with its regulations on identification and communication," said regional security analyst Carl Thayer.
Also, among the six Chinese rules is this warning: "China's armed forces will adopt defensive emergency measures to respond to aircraft that do not cooperate in the identification or refuse to follow the instructions."
Said Dr Thayer, emeritus professor of politics at the University of New South Wales: "If China sends military aircraft to challenge Japanese Self-Defence Force aircraft over the Senkaku islands, this would be a high-risk venture that could provoke a clash or cause an accident.
"Such an eventuality would be nothing less than a high-altitude game of chicken."
But Tsinghua University expert Liu Jiangyong, like many Chinese analysts, believes that China is acting within its rights, pointing out that Japan had taken over its own ADIZ from the US in 1969 and expanded it over the years.
"Japan's action is like adding a lock to a public place as the airspace over the islands is international airspace. If Japan can do it, why can't China do the same?" he said, dismissing as unfounded suspicions that China is using the zone to push its territorial claims.