If you google "nine-dash line", which violates UNCLOS, you'll understand why the ASEAN countries are upset and rightly so. China has visibly flexed their muscle in the region in recent years with building military bases, adding land to underwater islands so they can claim sea territory around them, and attacking fishing boats in disputed region. Some of this happen to dispute with Japan as well. With the economy not going well, I'm afraid this may be the Communist Party's strategy to diffuse tensions at home in order to hold on to power.