The most active September copper contract on the Shanghai Futures Exchange closed up 0.3 percent to 55,150 yuan ($8,700) per tonne on Thursday. The total open interest in Shanghai copper contracts stood at 584,278 lots, after the exchange double-counts the trades, near an all-time high of 605,514 lots on May 16.
"Prices are near the lowest level so far this year, and it's an increasingly heated battle between the bulls and bears on where the prices should go," said a Shanghai-based trader.