(As a side note, China doesn't get enough credit for what it did in 2008 to stabilize the global markets. It and the US literally spent their way out of what could have been a very brutal global recession)
Last year they bailed out HNA. Lots of chatter that HNA was bailed out because it had done some very high profile deals in the first world and China wanted to protect its reputation.
https://www.bloomberg.com/opinion/articles/2018-01-24/hna-sh...
The good news for the world is that Chinese corporate debt isn't held that much outside of China, due to tge double whammy of
1) investors valuing their chance of payback on a default like sovereign debt(large haircuts, very little leverage to get any say in the proceedings)
2) investors valuing the chance of a default like a corporate bond( much higher than sovereign defaults).
This means it has the worst of both worlds from a risk perspective but does pay a larger coupon. And if you are a distressed credit investor you have the same problem that is now an issue in most markets. You can be right about the default chances but the government could still swoop in and bail out the company making your fundamental analysis worthless.
The Chinese debt market tanking isn't going to hurt markets in a first order way. What could cause grief would be a scenario like the mid =80's where Japan almost on a dime stopped spending money around the world and brought it all back home to help fight their recession.
If China starts selling global assets, like housing in major cities around the world, and starts to decline their treasury holding rather than rolling them, then look out.