Copper stored in bonded warehouses in China, which don't disclose their stockpiles, comes to about 500,000 metric tons, said Goldman Sachs Group Inc. (GS)

Inventories have climbed by about 450,000 tons since November including both bonded stocks and those monitored by the Shanghai Futures Exchange, Max Layton, an analyst at the bank in London, said in a report dated today. Inventories held outside of bonded and exchange-tracked warehouses may have increased about 150,000 tons in the period, he estimated.

Copper stocks tracked by the exchange are the highest since at least 2003, figures showed last week, while inventories monitored by the London Metal Exchange are on course to shrink for a sixth month. Imports of the metal into China were the second-highest ever in February at 484,569 tons, customs figures showed March 10.

"We anticipate that the growth in Chinese copper inventories will end soon, with lower Chinese net imports expected in March as a result of lower ex-China availability and higher Chinese availability," Layton said.

Premiums for copper over exchange-traded prices signal that supplies in Europe and the U.S. are tighter than in China, Layton said. He predicted stronger exports of refined metal from the Asian country this month and in April and a "substantial" drop in imports.

European premiums have climbed to between $80 and $90 a ton from $30 to 40 in January, according to the bank.