Is a transit visa required for a South African passport holder.

Hello. I am a South African citizen living and working in South Korea on an E2 visa. I have a valid South African passport and Alien Regstration card both with more than 6 months validity. I will be travelling through Beijing en route to the Middle East and then through Guangzhou en route back to South Korea. In both cases I will be in China for less than 5 hours between flights and will not be leaving the airport. Will I require a transit G for China and if so, how do I go about obtaining it? Thank you kindly.