Xinhua, China's state run news agency makes it clear what China's position in the dispute is.  Here is an excerpt from Chosun newspaper (couldn't find an english version of the Xinhua article):

When we look at history, Dokdo has been recorded as Korean territory since 512 A.D., while Japan began considering it Japanese territory from 1905… – Xinhua News Agency

While China has their own territorial dispute with Japan and the current Chinese government has been accused of rewriting history just like Japan, my own bias tells me they are being truthful here.