This is very interesting that the Chinese government has apparently given the US the go ahead to attack North Korea in response to a strike against US soil, but not to the extent that it leads to regime change:
China won’t come to North Korea’s help if it launches missiles threatening U.S. soil and there is retaliation, a state-owned newspaper warned on Friday, but it would intervene if Washington strikes first.
The Global Times newspaper is not an official mouthpiece of the Communist Party, but in this case its editorial probably does reflect government policy and can be considered “semi-official,” experts said. (…..)
“China should also make clear that if North Korea launches missiles that threaten U.S. soil first and the U.S. retaliates, China will stay neutral,” it added. “If the U.S. and South Korea carry out strikes and try to overthrow the North Korean regime and change the political pattern of the Korean Peninsula, China will prevent them from doing so.” [Stars & Stripes]
You can read more at the link.