It doesn't get a whole lot of mention in the press, even in the midst of the current controversy, but there are actually three nuclear powers with territorial claims on Kashmir; China grabbed a piece of it in 1962, and Pakistan ceded another sliver of territory the next year.
I'm honestly not sure what the Chinese interest is in all this. On the one hand, they have been partners with the Pakistani nuclear program --- it's even rumored that they gave them the design of for a working warhead. The Chinese also have plenty of reasons to be annoyed at India, with which they have several disputed stretches of border; India has also annoyed the Chinese by, for instance, playing host to the Dalai Lama, a perpetual thorn in their side. So, the Chinese have plenty of reasons to want to see India taken down a notch, which may well have been the idea behind aid to Pakistan.
On the other hand, China can't be thrilled with the Pakistani-sponsored Muslim separatists in Kashmir, given that they have a Muslim separatist problem of their own. To have that appear to succeed would set a precedent that the Chinese would not like to deal with within their own borders.
On the third hand, it could be that some within China see not one, but two potential regional rivals in this conflict, and would not be displeased to see a plague on both their houses, radiation sickness working as well as anything else. (Which would also be a line to use against the separatists --- "See? See what this leads to?"). But then, of course, there might be a refugee problem.
So what's really going on? I don't know. I don't pretend to know. But it's obvious that they're involved, if only by virtue of common borders and their history of aid to Pakistan --- and they're quiet. Too quiet.