Hong Kong day trip to Guangzhou

You will need to apply for a visa if you want to go to Guangzhou. You can do that in Aus, or in HK.

If that is a separate trip to the Shenzhen visit, ensure you get a double entry visa. #

If you only want to go to Shenzhen you can get "a single-entry five-day Special Economic Zone Tourism Visa on arrival for ¥168-1,000. At the Luohu border (罗湖口岸), the office is immediately upstairs after clearing the Hong Kong immigration and customs. It is open 9AM-11:30PM seven days a week and only accepts RMB for payment. It can be reached at +86 755-8232-7700 for enquiries. Currently, these visas are available for Australian, Canadian, New Zealand and most EU countries passport holders. Note that the charge for UK passport holders is much higher at ¥469 for a five-day Shenzhen-only visa, while it costs only ¥168 for most other nationalities. " From Wikitravel

David, if you book an organised tour made by a travel agency registered in Hong Kong, you don't need a visa to visit the the Pearl River Delta region (Guangzhou, Shenzhen, Zhuhai, Foshan, Dongguan, Zhongshan, Zhaoqing, Huzhou Municipalities) for up to 6 days.

Does the tour company tell you that it will organize a Group Visa for you?