In Xinhua's Chinese language version of the article, the colonel [Shen Jenke] said the aircraft would "strengthen the monitoring of targets in the air defence zone and do their duty".
I would now interpret this as Xi Jinping having miscalculated initially. No response at all to the first two overflights and now fighters? Chinese are very sensitive to humiliation and the Japanese and Korean overflights are being seen as humiliation. Chinese pride, insecurity and stubbornness--and Xi's own standing--are now being reasserted. Has Xi thought through what happens next? What are the fighters going to do if another overflight occurs? What is the Chinese fighter pilots "duty" in another overflight? Isn't a fighter pilot's duty to shoot down foreign jets? Is Xi going to shoot down foreign jets? What then would the other country--the U.S., Japan, South Korea--do? Has Xi an expectation what that will be?
This is China's doing, sure as shootin'. And I don't think Xi is sure what he has done. What should other countries do? I don't think resume the overflights. China has backed itself into a corner but it's still backed into a corner. My first reaction to the initial U.S. overflight was "Why?" It has now been done twice by three countries combined. Don't poke at a guy when he's in a corner. How about taking a page from the Cuban Missile Crisis? Tell China privately that if it rescinds this defensive air zone announcement, they, the three other countries, will honor it. Make it reciprocal: China must notify Japan when it intends to send military aircraft into the area (part of which is also a Japanese air defense zone). What if Xi wants a shooting fight out of this? What if, in other words, he did anticipate precisely this action-counteraction escalation? Then the question becomes, is that what Japan, South Korea and the U.S. want, also? I cannot believe that it is. This would go down in history as one of the dumbest reasons for countries to begin shooting at each other. China looks really bad right now: reckless, prideful, stubborn, stupid. Obama and Kerry said recently they "don't think" they, Obama and Kerry, are "stupid." Reasonable people can disagree on that one in general. On this one in particular I hope they are not stupid.