China stressed on Wednesday its ability to "effectively manage and control" its newly declared air defence identification zone, a day after it calmly handled an unannounced US entry into the zone.
On Tuesday, China monitored two US B-52 bombers that entered the zone without informing Beijing, the Defence Ministry said. The Foreign Ministry said on Wednesday that other air defence identification zones will be set up "at the right time when preparations are ready".
Responding to the US flights, Defence Ministry spokesman Geng Yansheng said: "The Chinese military monitored the entire process, carried out identification in a timely manner and ascertained the type of US aircraft.
"China is capable of exercising effective control over this airspace."
The US aircraft flew south and north along the eastern border of the East China Sea Air Defence Identification Zone from 11 am to 1:22 pm on Tuesday, about 200 km to the east of the Diaoyu Islands, Geng said.
The B-52s took off from their home base in Guam in what US defence officials say was a routine exercise. Experts said Japan and the US have been overreacting to, and imposing double standards over, China's zone.
Zhang Junshe, a military expert, said the main purpose of setting up the zone is to identify aircraft entering the area.
"Tuesday's case showed that we have finished the task and cut the time to launch an early warning."
Foreign Ministry spokesman Qin Gang said on Wednesday that China will respond according to the degree of threat posed by aircraft entering the zone without informing it.
Yin Zhuo, a senior naval expert, said setting up the zone will not add to the possibility of conflicts over the East China Sea. Instead, it will reduce risks by introducing transparent measures.
If a foreign aircraft is flying toward China's territorial air space at high speed and threatening China's territory, Beijing could take relevant action, Yin added.
China announced the establishment of the defence zone, which covers the Diaoyu Islands, on Saturday.
It requires aircraft to provide a flight plan, their identification and to maintain two-way radio contact to respond to identification queries from Chinese authorities.
Beijing said it could take emergency defensive measures against aircraft that do not comply, while Washington has said it will not meet the Chinese demands.
More than 20 countries, including the US and Japan, set up their own air defence identification zones decades ago.
The US formally defines such a zone in the Code of Federal Regulations, which states: "No person may operate an aircraft into, within, or from a departure point within an ADIZ, unless the person files, activates and closes a flight plan with the appropriate aeronautical facility, or is otherwise authorised by air traffic control."
Xinhua News Agency said in a commentary on Monday, "Japan set up such a zone in the 1960s and it even one-sidedly allowed the zone to cover China's Diaoyu Islands."
Rana Mitter, an expert at Oxford University on Sino-Japanese relations, told Agence France-Presse he feels China's tough stance on issues related to the Diaoyu Islands "clearly regards its own territorial claims as having been underplayed and understated in recent decades and is now looking to reverse the situation".
Taylor Fravel, an expert at Massachusetts Institute of Technology on China's territorial disputes, said the immediate trigger for Beijing's declaration of the zone may have been Japan's threat to shoot down drones after an "unidentified unmanned aerial vehicle" flew toward the islands.
Fravel said China has likely viewed Japan's own zone as being expansive.
Japan's Yomiuri Shimbun newspaper reported on Wednesday that Tokyo has decided to expand its zone. So far, Washington has not objected to the plan.
Zhang said Japan's plan to expand its zone shows it is exercising double standards on the issue.
Li Jie, an expert at the Naval Military Studies Research Institute of the People's Liberation Army, said that by sending the bombers, "the US wants to make sure that its reconnaissance and intelligence gathering on China can continue".
Washington also used the move to show its strength to ensure its status in the Asia-Pacific region, Li said.