So there is no choice but to make China held accountable in some way. The pressure on China is to be applied, starting with sanctions on Chinese business entities doing business with N. Korea.
To the surprise of China, that is what happened:
China is voicing concerns after U.S. President Barack Obama signed a bill imposing tougher sanctions on North Korea.
The bill, which aims to cut the last remaining lifelines to Pyongyang’s nuclear weapons and missile technology, will blacklist third-party individuals and entities that engage in North Korea trade.
Many of the targets are likely to be Chinese enterprises. Banks and trading firms along the North Korea-China border with offices in Dandong would be found in violation of U.S. sanctions.
http://www.upi.com/Top_News/World-News/2016/02/19/China-Sanctions-wont-resolve-North-Korea-tensions/7811455890709/
If China ended up breaking a recalcitrant Kim dynasty by sanctioning oil and food, the result could be extraordinary hardship and armed factional combat followed by mass refugee flows across the Yalu - multiply the desperation and number of Syrians heading to Europe. Then toss in loose nuclear weapons and a possible South Korean/U.S. military push across the Demilitarized Zone to force reunification.
The result would be a first-rate nightmare for Xi.
Beijing, in response to the criticism, pushed back, taking the position that it is America’s responsibility to solve the nuclear issue, not China’s. In effect, China absolved itself of responsibility to support international efforts to curtail Pyongyang’s nuclear weapons program and essentially declared that North Korea was not its problem.
The Obama administration, however, is about to make it so. It is now persuading Seoul to accept and deploy the Terminal High Altitude Area Defense system. THAAD, stationed in China’s neighborhood, will give the US the ability shoot down North Korean missiles - and help knock down Chinese ones. Beijing summoned the South Korean ambassador over the missile-defense discussions with the US, and a senior diplomat said THAAD makes China “furious”.
Now that the South Koreans appear amenable to accepting THAAD, Beijing is beginning to reconsider its refusal to apply pressure on Pyongyang. Although China is still trying to deflect responsibility, American policymakers may have found the key to bringing Beijing around.
http://www.worldaffairsjournal.org/blog/gordon-g-chang/could-missile-defense-plan-turn-china-north-korea