"Last week China’s foreign minister warned the U.S., South Korea and North Korea could be heading for conflict." - Since China pulls Kim Jong Dum's strings, he would know. They don't want a missile defense system on their border, and they don't want a reunified Korea with the US as an ally. 
China is running out of options, do they let NK start a war that will inevitably draw them in and risk the downfall of their own government or do they let NK collapse and reunify with SK. They prefer the status quo to either. It will depend on how bad they want that missile defense system gone.