This is undoubtedly a salami-slicing tactic. After repeated probing, international public opinion will become desensitized and eventually accept the possibility of Japan acquiring nuclear weapons.They have just chickened out.
Still China should question Japan's true intensions and at least make a complain to the IAEA. Give them another chance to show their true colours first. So that if China needs to activate the UN Enemy State Clause, it had already exhausted all peaceful options first.
China and other friendly nations must develop effective responses and contingency plans to Japan's nuclear ambitions.