Imports of copper and products by China, the world's largest consumer, unexpectedly climbed for the first time in three months.

Purchases increased to 399,052 metric tons in September, China's Customs said yesterday. That's 23 percent more than August, according to data compiled by Bloomberg.

Copper, used in pipes and power cables, has doubled in London this year as China's stimulus spending and State stockpiling boosted imports to a record, and the world recovered from its worst recession since World War II, increasing demand for raw materials.

"The number was substantially stronger than we'd expected," said Zhao Kai, an analyst at Jinrui Futures Co. "We'll need to see whether some of these shipments will be re-routed to somewhere else or came under tolling practice" before determining the nature of the rebound.

Tolling refers to tax-free imports of refined metal in exchange for exporting the processed products. Export data is scheduled for release on Nov 26.

"It could be that Chinese domestic inventories were not as high as people thought," Zhao said. China had "almost zero" copper inventory at the end of last year, he added.

The copper surplus in China so far this year may be as much as 1.2 million tons after a "very unusual" surge in first-half imports, researcher Beijing Antaike Information Development Co said on Sept 25. The estimate included State Reserve Bureau purchases, Antaike's senior analyst Li Yusheng said. The bureau's buying totaled 235,000 tons, according to a Caijing magazine report.

Copper for delivery in three months on the London Metal Exchange rose 2 percent to $6,260 a ton at 1:53 pm Singapore time. The metal for January delivery on the Shanghai Futures Exchange increased 0.5 percent to 49,110 yuan a ton.

"Everybody's caught by surprise" because the market widely expected a month-on-month decline in September imports, said Zhou Qian, an analyst at commodities researcher CBI China Co.