Aug. 18 (Bloomberg) –Stockpiles of copper held in bonded warehouses in China, the world's biggest user of the metal, may have rebounded since June as imports increased amid a lull in manufacturing over the summer.

Inventories in the warehouses, which aren't disclosed, may have gained by about 100,000 metric tons over the period to 400,000 tons, according to estimates from traders and analysts in China including Cofco Futures Co. The stockpiles, stored in the warehouses before clearing customs, slid to a year-to-date low of about 300,000 tons in June from a record of 600,000 to 650,000 tons in March, the analysts and traders said.

Higher stockpiles in China, which accounts for about 40 percent of global demand, may curb an expected gain in imports this quarter, hurting prices. Copper on the London Metal Exchange has slumped from a record in February as concern that global growth may be slowing outweighed forecasts for a deficit.

"Because demand in July and August is usually sluggish, imports accumulated in warehouses," said Peng Qiang, a Cofco Futures analyst. "We'll have to wait till September to see how demand can absorb the rising supplies," Peng said from Beijing.

Three-month metal on the LME peaked at $10,190 per ton on Feb. 15 before tumbling 17 percent to an eight-month low of $8,446.25 on Aug. 9, joining a slump in equities and commodities that fell on concern the global economy may be faltering. Copper traded at $8,920 at 12:50 p.m. in Shanghai, 0.5 percent lower.

Increased Holdings
The amount of copper held in separate warehouses monitored by the Shanghai Futures Exchange, which is disclosed, has also surged over the past month to reach the highest level since May. Holdings have risen 35 percent since July 7, gaining for five straight weeks to 120,819 tons last week, bourse data show.

China's copper imports climbed last month to the highest level since January, with arrivals of the refined metal, copper alloy and products rising 9.5 percent to 306,626 tons from June, the General Administration of Customs said on Aug. 10. Over the first seven months, shipments totaled 2 million tons, 22 percent lower than in the same period last year.

China's refined-copper output climbed to an all-time high of 478,000 tons in July, 18 percent higher than a year earlier, according to China's National Bureau of Statistics. Still, output of copper products, a gauge of demand, fell to 959,000 tons last month from a record of 1.05 million tons in June.

Market Turmoil
Buying by Chinese copper importers on dips helped to underpin prices during recent market turmoil, said Pang Ying, an analyst at Shenzhen Rongtuo Trading Co. Inbound shipments of copper may also continue to rise in the next couple of months as so-called arbitrage trading, buying the metal in London and selling it in Shanghai, has become profitable, Pang said.

Copper for November delivery on the Shanghai Futures Exchange traded at 67,210 yuan ($10,520) per ton at 11:30 a.m. in Shanghai today.

Global copper inventories tracked by the LME fell for three consecutive weeks to 461,775 tons as of Aug. 12, and totaled 464,625 tons yesterday. Stockpiles in Asia were unchanged at 173,575 tons yesterday, equaling the lowest level since April.

While a strengthening yuan made raw-material imports priced in dollars cheaper, the currency's gains may also make Chinese exports of products more expensive, according to Ren Gang, head of research department at Maike Futures Co.

"A knee-jerk reaction to a strengthening yuan is negative for domestic prices, while positive for London, but in the medium term, as exports of downstream products such as air- conditioners are hurt by a stronger yuan, so-called Chinese demand will be affected as well," said Ren.

The People's Bank of China set the reference rate for the yuan against the dollar at a record 6.3925 on Aug. 16. The rate was set at 6.3942 today.