Aluminum Corp of China Ltd (Chalco) , the country's top aluminium producer, posted a first-half net loss of 623.8 million yuan ($101.9 million), hurt by lower prices and oversupply in the world's top producer and consumer of the metal.

The result compared with a net loss of 3.25 billion yuan in the six months through June 2012, the company said in a filing to the Shanghai stock exchange on Friday.

Oversupply problems prompted the company in June to temporarily close 380,000 tonnes of annual aluminium capacity, representing 9 percent of its annual output in 2012.

Global production of the lightweight metal used in packaging and transport has consistently outweighed demand, leading to a build up of inventories and hitting prices.

World prices of aluminium hit four-year lows below $1,800 a tonne in late June. Prices have since recovered to $1,836 but are still down about 11 percent so far this year.

In China, spot aluminium prices AL-A00-CCNMM fell about 4.5 percent in the first half of 2013. The price stayed at three-year low levels of about 14,300 yuan per tonne on Friday.

Chalco produced 6.08 million tonnes of alumina in the first half of the year, up 1.84 percent from the same months last year. Alumina is used to produce primary aluminium. The firm's primary aluminium production inched down 0.49 percent on-year to 2.03 million tonnes, the exchange filing said.