What makes a superpower? Nuclear weapons and military capabilities? If so, China is much closer to Russia than to the United States. Economic strength? If so, then we should also consider Japan, Germany, and France for nominations as 'superpowers'.

From wikipedia:

Alice Lyman Miller defines a superpower as "a country that has the capacity to project dominating power and influence anywhere in the world, and sometimes, in more than one region of the globe at a time, and so may plausibly attain the status of global hegemony."
What is 'dominating power and influence'? Is it the capability to unilaterally press one's agenda on another state? If that's the case, then it precludes the United States, since the US cannot exert 'dominating power' 'anywhere in the world' (i.e. Crimea). According to realist IR, relative power is more important than absolute power, and therefore thinking in those terms, I think we can come to a better understanding if China (or any other state) is truly a 'superpower'.

According to a national power index I am developing, the power of the top 3 states (US, China, Russia) is statisically distinct from the next 7 (Japan, France, UK, Germany, India, Brazil, Italy). If we move Japan from the second group to the first one, there is still a major difference, so perhaps we should consider Japan a candidate as a 'superpower' as well.

It's not until we reach #5, France, that the difference between the top powers and the next tier becomes more similar. So I would say that yes, China is a superpower, insofar it's ranked as the second strongest state on my index and is in the top category of powers that also include the United States (#1), Russia (#3), and Japan (#4). But that should also tell us something about the nature of a 'superpower'; it's not necessarily predicated on one profile of capabilities.