The central principle of China's foreign policy is stability. China has supported North Korea's communist government for the last thirty years mostly as a defense buffer zone on it's northeastern border. But North Korea is no longer acting as a buffer. Now it has become as source of regional instability. That is trouble. A nuclear warfare crisis on China's border is a bigger nightmare for them than it is for the United States. And the Chinese government will eliminate Kim in a heartbeat if they see the opportunity.