Very big indeed and capable of launching long range counter atacks.  And don't forget Russia will absolutely come in.  Russia can't stand up to the US and the West if China is out.  China also has the means to deliver nuclear weapons not just to the land, the ocean but to the heartland of America as well. If its national survival is at stage due to the war with the US, I have no doubt China will turn to nuclear war and America is to blame for all the deaths and the collapses of economy. I never heard US ever went to war with any nuclear country.  And China is just simply too big to stage anything in South China Sea.  Maybe a small conflict then both sides will deescalate quickly.  Donald Tump is not that stupid.