Graham Allison, director of the Belfer Center for Science and International Affairs at Harvard's Kennedy School, wrote an oped for the 26 March 2013 issue of The Atlantic titled "China Doesn't Belong in the BRICS." He based his argument on the disparity of China's economy compared to the other members of the BRICS--Russia, India, Brazil and South Africa. He referenced China's much higher GDP, GDP growth rate, merchandise exports, and foreign exchange reserves. I raised some of the same issues in my March 18 posting below titled "BRICS and Africa."
As the BRICS are intended to represent developing economies, one could ask the same question why a northern industrial country like Russia is included. If you eliminate both China and Russia, that leaves only India, Brazil and South Africa and they already have their own organization--the India-Brazil-South Africa (IBSA) Dialogue Forum.