Your go to place for regional North Korean nuke test responses is Sino-NK. Here’s an assessment of China’s policy responses. Here’s a translation of an editorial warning to Pyongyang by Chinese NK expert Zhu Feng shortly before the test (an edited/censored version was later reprinted in China, but it’s interesting that Zhu’s more strident original warning was allowed to be distributed globally via the Singaporean press). And here we have a roundup of South Korean press response, including this possibly disturbing statement from the Chosun Ilbo, voice of the conservative South:
...the only hitherto untested alternative [to other attempts to restrain NK] is the combined power of the United States and China. Ergo, South Korea must now seek a way of forcing this union into existence. The only way to do this, it says, is to ensure that both countries are aware of how close Seoul is to going nuclear.
Greater Sino-Us co-operation is in fact a common theme in all of the above, including Chinese sources. How that plays out against the ‘pivot’ and in respect of all the other territorial disputes across the region remains to be seen.