I can't find a "no first use" of nuclear weapons clause. I assume that they still feel they are free to use nuclear weapons in response to a conventional attack.

No doube, China's nuclear weapons stock is far too small to constitute an effective deterence. US and Russia have more than 3000 for immediate use and have nuclear material and capability to produce 10's of thousands more. China needs to have a couple of thousands for immediate use if it wants to be taken seriously by the 2. And must stock-pile materials for far more.