Can I apply for chinese visa without invitation letter?

Hi, this is Franscine again. I would just like to ask if it's possible to get a Tourist Visa even without an invitation letter from a Chinese national? I am visiting a friend in china who is on business visa and plan to go sightseeing with her for a few days. I have already booked flights and I am worried my visa application will get rejected. Please advise what other supporting documents I could include in my visa application. thank you.