Question is, would they actually do it? Or would they just pull a Medvedev and keep repeating "technically we could nuke you"?
I understand China finds it important to constrain itself to international law to retain a moral high ground. But Russia did the exact same thing with regards to Ukraine and it didn't amount to much in their defense. At least I suppose now history is judging them favourably for it.
Any first strike will mean war, and I think it's in China's interests (and foreign policy style) to wait for the first strike to come from the enemy and react.
sometimes combined with 
