The most scary path would be intentional. I can't think of any other aftermath except for WWIII.
Yeah sure. We've just lost 3 million lives, let's kill the rest of the planet as consolation. As fucked up as our politicians are I hope they are not ready to die.
More likely result is that most of the world would stop trading with them. Nobody would want to see a Made in China tag on anything. Which would in turn be very bad for the economy in China and lead to unrest.
So the more likely outcome would be civil war in China.