I would not be surprised if most countries that have nuclear weapons have many more nukes then they publicly admit and what they agreed to. I don't think this is something unique to china.
I don't even know why we are building nukes, it's so retarded. No one will use them, since we know that if one is launched, a retaliation nuke from the enemy will follow, and we shall destroy the earth with nuclear warfare. They're just built to threaten and scare people, but if there is some error, or an idiot launches them, the world is finished.