Imports of refined copper and copper products by China, the world's largest user, tumbled 34 percent in October from the previous month as stockpiles built up.

Purchases declined to 263,109 metric tons last month, the customs office said today. That's the lowest monthly total since January's 232,700 tons, according to data compiled by Bloomberg.

Copper, used in pipes and cables, has doubled in London this year as China's 4 trillion yuan ($586 billion) stimulus spending, state stockpiling and a lack of scrap material boosted China's imports to a record. Stockpiles in duty-free warehouses may have risen to 350,000 tons from almost none at the start of the year, Xi'an Maike Metal International Group said on Nov 9.

The magnitude of the decline in monthly imports "is big, yet is expected due to prices," Zhou Qian, an analyst at Shanghai-based commodities researcher CBI China Co., said today. "It confirms our expectation for a slowdown."

Three-month copper in London traded at $6,601 a ton at 4:30 p.m. in Singapore, while Shanghai futures closed at 50,910 yuan ($7,458) a ton today. Buying the metal from overseas to sell in China incurs a loss of more than 1,300 yuan a ton after accounting for local taxes, according to Bloomberg calculations.

China's scrap copper imports were 260,000 tons in October, customs said. That compares with 411,696 tons in September, according to data compiled by Bloomberg.

To be sure, "we don't think the fall in imports will cause a slide in London prices because it's largely expected," Chen Xiang, an analyst at Dahua Futures Co. said from Shanghai. "Demand from developed markets is expected to pick up."

Aluminum and products imports by China slumped 56 percent to 86,611 tons in October from a month ago, customs data showed.