Do I need a visa to go to Shenzhen (part of China)?

I'm a South African, planning to go to Hong Kong. From there, I plan to spend a day at Shenzhen only (not going to other parts of PRC). Do I need a visa for Shenzhen (PRC)? I read elsewhere online that I might have to get a 5-day VOA at Shenzhen border - is it true? Thank you!