Good read for those underestimating China:
http://www.businessinsider.com/chine...?client=safari
A big advantage highlighted in the article is that China could mobilise from one position, while the United States have forces spread out all over the world.
They're considered very close in power, and the allies of the US are not as powerful as the ones China has (and the US would have to give up a significant number of strategic positions to focus on China).
It would be a disaster for the US.