Aluminum stockpiles in the main trading regions in China have climbed to the highest level in two years as growth in supply outpaces demand in the world's largest user, according to two industry surveys.

Reserves in Shanghai, Wuxi and Hangzhou, and in Guangdong provinces gained to about 940,000 metric tons as of Oct 22, the highest since September 2010, according to Wen Junxiang, head of the research department at Guangzhou KT Commodity Information & Consulting Co. Stockpiles more than doubled this year to about 1 million tons, the largest since July 2010, said Zhang Chenguang, an analyst at data provider SMM Information & Technology Co.

The estimates add to signs of a glut as new capacity, especially in the West, helps boost output to the highest ever even as China's manufacturing shrinks. Aluminum in London has dropped 12 percent over the past year, and Alcoa Inc, the largest US producer, cut its forecast for global demand growth this month as China's economy slowed.