Copper sales by China's stockpiling agency were designed to lower prices, protect processors and curb excessive investment in the industry, the Beijing Youth Daily said, citing Chang Qing, vice chairman of the China Futures Association.

　　The State Reserve Bureau sold the metal to ease shortages and ensure production isn't disrupted at copper processing plants, the report said. Some copper stocks at SRB warehouses were bought in the 1990s and it is time to sell, the report cited Chang as saying.