re: Invitation Letter

I will travel to China from March 6th to March 10th: 2 days in Guangzhou and 2 days in Hong Kong. I plan to fly into Guangzhou, travel from Guangzhou to HK by rail and return back to Japan from HK.

I have filled out the necessary paperwork and plan to submit it to the Embassy 2019.02.01. My question is:

My Chinese friend in Guangzhou must write a formal invitation / document? This must also be submitted with my application? If it is a personal travel plan, they must also write the dates and details of our travel?

Please advise.
Many thanks in advance.