No, you need to either leave with your original passport, visa and entry stamp OR you need to first go to PSB and get the necessary paperwork to leave. I doubt very much that if you entered on a non-Spanish passport that they will process a Spanish passport. You would need a replacement passport of the same nationality on which you entered China.

Further, you are required to have your passport or resident ID with you when out and about: there might be a random police check.

Your best bet here is to contact the relevant embassy and ask for consular assistance.