For the week ended October 9, exchange warehouse copper stocks rose 2,614 tonnes to 99,369 tonnes. The exchange will report stocks again on Friday. It is frustrating to see the stocks crowding the 100,000-tonne mark," one trader said.

Neither the government's much vaunted infrastructure projects nor an export drive had made a dent in stocks, he said. China has launched a massive package of infrastructure projects, including wiring far-flung rural areas, to energise flagging economic growth.

In August, the government also allowed 50,000 tonnes of refined copper to be exported at a 5.0 percent tariff instead of the regular duty of 30 percent.

An analyst said that copper fabricators were accumulating stocks faster than cathode producers, and stocks of copper wire would have to be drawndown first.

"The downstream overcapacity is more serious than in the upstream sector," he said.

The regional financial crisis had seriously affected China's export of copper materials, because more than 90 percent of its copper material exports went to other Asian countries.

The drive to sell copper cathode so far had proved disappointing because of the slump in world copper prices, traders said. Three-month copper on the London Metal Exchange (LME) fell to a 12-year low of $1,577 a tonne early this month and has been trading barely above $1,600 this week.

Traders said some of the Shanghai copper stocks deliverable to LME warehouses had found their way to Singapore, but the amount was unlikely to be very large.

Since the start of September, a total of 55,325 tonnes of copper had been delivered to Singapore as of last week, according to figures compiled by Rudolf Wolff & Co.

"Some of the Shanghai warehouse stocks were booked at 18,000 yuan, and producers are loath to export them at 16,000," atrader said. "They prefer to wait for prices to recover somewhat."

Shanghai copper for January delivery traded at 15,800 yuan ($1,908) a tonne on Thursday morning.

Some traders attributed the rising stockpiles to the planned merger of futures exchanges, as the copper stocks were moved from other depots to warehouses of the Shanghai Metal Exchange, which would be the sole exchange trading metals.

But other traders said the bottomline remained a lack of demand.

"If there's demand, the copper should have been drawn down, rather than being moved around," one trader said.