The traffic rules for circles in South Africa are as follows:

Mini Circle

Regulatory Sign R2.2

The above sign is an indication of a MINI CIRCLE and according to the traffic rules, this works in a similar way to a 4 way stop. First person to the relevant point, first to ride. Or in the words of the website Arrive Alive - "Slow down and give way to other vehicles that cross any Yield line before you do. Proceed in a clockwise direction around the painted island, without driving on it."  

Do not confuse the MINI CIRCLE with a traffic circle or round about which works on the basis of yeilding to traffic coming from the right. It's sign is:

For more information hereon you can go to any the following links:

http://www.circles.org.za/r2.html#

http://www.arrivealive.co.za/pages.aspx?i=2163

http://roadsafety.co.za/2010/02/11/easy-steps-to-understanding-traffic-circles/