Are there any visa requirements for return travel between Guangzhou & Hong Kong?

I am a Singaporean passport holder flying into Guangzhou for leisure. I plan to make a return trip from Guangzhou to Hong Kong and then back to Guangzhou again. I will then fly out of Guangzhou. Total length of stay is less than 15 days. Is there any requirement for entry permit for the Guangzhou-Hong Kong-Guangzhou leg?

JJ