I'm a Colombian citizen working in Italy with a 2 year work permit, and I'd like to go to Beijing.

You can apply from the CVASC branches in Rome or Milan. Your passport, filled application form together with a recent passport photo, confirmed return air ticket and hotel reservation in Beijing are required. If you can provide the invitation letter, the air ticket and hotel reservation are not required. Another important document is your work permit. You need to provide it when you submit your application.