Anjin, the second Chinese mining company operating in the Marange area, started mining in October last year.
The Marange area is at the centre of diamond export controls by the Kimberly Process for suspected human rights violations in mining of the precious stones.
The government says it has sold $313 million worth of diamonds produced by two companies in Marange since last year. There are five firms with licences to operate in Marange, two of them Chinese.
"Anjin are stockpiling, and they now have about 1 million carats. They are now waiting for inspection and certification from the Kimberly Process to start exporting," Gift Chimanikire, deputy mines minister told the Herald newspaper.
Rights groups have pressed for a ban on the Marange alluvial diamonds, accusing security forces of killing hundreds of the over 30,000 illegal diggers who descended on the poorly secured fields in 2006.
The government, meanwhile, has said companies in Marange, including Anjin, will be exempt from regulations published last month that force mining companies to submit plans on how they intend to transfer control of a majority of shares to local blacks within six months.