Can I get an extension to stay until middle of Oct from a local PSB within China?

David, you wanna get about a 45-day extension, right? It's possible to do so. You need to apply for extension at the Exit & Entry Adminsitration seven days before your current allowed stay duration runs out. You need to submit your passport, an application form, a recent photo, a registration form of the temporary residence, and an invitation letter from a relevant entity or individual.