China unveiled a unified stock index to track both markets in Shanghai and Shenzhen in April, a move likely to open a floodgate for more trading derivatives such as index futures. The new index, with 300 component companies traded on Shanghai and Shenzhen stock exchanges, will be the first of its kind on the mainland. The index members will be the largest 300 stocks - 180 from Shanghai and 120 from Shenzhen - in terms of market capitalization,