North Korea is at its wits' end now.

http://www.reuters.com/article/us-northkorea-china-envoy-idUSKBN1670BP?il=0

Coal export to China constitutes 1/3 of North Korea's incomes.  Therefore, coal import ban from China will affect North Korea tremendously.  North Korea's coals are of high quality because they're non-smoke coals which don't produce smogs.

The next weapon China has is OIL export ban to North Korea.  This will crumble NK.