Exports to China, which overtook the United States as Japan's top market in 2009, fell 14.1 percent in September from a year earlier, the biggest decline since January. Shipments to the European Union also dropped a striking 21.1 percent as Europe's debt crisis remained firmly entrenched. "The export data for September was particularly poor," said Natixis strategist Nic Brown.

"And if you look at the way in which Japanese exports are a function of the demand from the rest of Asia - that's become clearly apparent over the last couple of years - this is a reflection of weakness in the Asian economy as a whole."

Three-month copper on the London Metal Exchange closed 0.8 percent weaker at $7,953 per metric tonne after touching an intraday low of $7,930, the weakest since September 7.

The metal, used extensively in construction and power, has broken below its range of $8,000 and $8,400 held since early September, which may prompt further liquidation of long positions, traders said.

In September, Beijing announced plans to spend $157 billion on infrastructure projects, but those are likely to be on hold until China's once-in-a-decade leadership change is finalized next month and the new leadership takes over next spring.

"The question is, how much longer do we have to wait until the new political team is genuinely in charge and starting to make decisions?" Brown said.

HIGHER ALUMINIUM SURPLUS: Also indicative of sluggish Chinese downstream demand for copper are rising stocks in warehouses monitored by Shanghai Futures Exchange, which by Friday had jumped more than 8 percent on the week and 48.5 percent since early June.

"The rise in inventories was due to China's sluggish downstream demand for copper, as well as its recent high copper imports and output levels," said Great Wall Futures Analyst Li Rong.

Data on Monday showed Chinese copper production in September matched its second-highest level this year as tight scrap supplies and favorable export policies encouraged smelters to keep output high.

China's imports of copper rose 11 percent in September on the month to 394,837 metric tonnes (435,233 tons), the General Administration of Customs said last week.

In aluminum, data from the International Aluminum Institute showed global daily output rose slightly in September to 67,000 tonnes. Analysts said this showed that needed capacity cuts were not occurring despite estimates that 30-40 percent of producers were loss-making.

Even before the data was released, BNP Paribas analyst Stephen Briggs had increased his forecast of the global surplus.

"Due to softer than expected demand and with few fresh smelter cutbacks having been announced in recent months, we have raised our forecast of the physical surplus in the aluminum market in 2012 to 750,000 tonnes," he wrote in a note released on Friday afternoon. "This may take the cumulative surplus in 2008-12 to nearly 9 million tonnes."

On the LME, three-month aluminum closed 0.5 percent lower at $1,960 a tonne as LME aluminum stocks rose by 23,750 tonnes to 5.06 million tonnes, close to the record of 5.13 million touched in February.

Tin tumbled 3.9 percent to end at a near-one-month low of 20,450 a tonne, zinc lost 1.5 percent to finish at $1,856, lead fell 2.1 percent to $2,070, and nickel gave up 2.2 percent to $16,590, its weakest since September 13.