China is not on par now in military and diplomacy with the USA, so it isn't a superpower yet. However I think it will not last that long before China is the strongest superpower.
It is building strong links with Brasil, Russia, India & South Africa (BRICS) and they are making a lot of unilateral deals with many nations in Asia & Africa, taking over the lead there that Western nations had. It's economy and technology is becoming very good. 12.8% of global research and development they do, well ahead of England and most of Western Europe. Their army is indeed defensive, but it is growing and gets influence in South Chinese Sea and Indian Sea.
There are many problems they have (minorities, high educated citizens, but no democracy, USA being stronger in the military (so do must avoid real military confrontations)), but when coped it is over with USA being the world sheriff.
Read more about this Tomgram: Pepe Escobar, Inside China's "New Normal".