My son is marrying a Chinese national in BC, what do we do to get the marriage recognized in China?

This summer my son and his fiancee , a Chinese national, are coming to BC to get married in July. They want to know what needs to be done to make the marriage legal in PRC. They heard something about getting the marriage certificate notarized and take it to the Chinese consulate, but they will not be here for very long this summer. Can we send the certificate to them and they take it somewhere over there? or does it have to be done before they go back?