Shanghai Futures Exchange (ShFE) copper ended the session up 1.6 percent at 36,260 yuan ($5,504) a tonne. Signalling shorts closing out positions, market open interest has shrunk to its lowest in nearly two months, ShFE data showed. Copper's outlook has been darkened by a surplus of supply, leading traders to their short positions, or bets that prices will fall. China, the world's top producer of the refined metal shipped out a surfeit of metal at home. China exported 84,959 tonnes of copper in May, up by 256 percent from the same month last year.
"The (export) jump has largely been prompted by Chinese refiners shipping metal into the bonded warehouse network, which is in turn being exported in order to keep the domestic market tight amid rising domestic refined production, which has ... supported the draw downs in ShFE copper inventories," Citi said in a note.