China, the world's biggest consumer of solar-grade polysilicon, will tighten up on imports of the material after solar manufacturers took advantage of a rule that allowed them to avoid duties.

From September, it will suspend applications from solar companies to import polysilicon under the so-called "processing trade" rules, whereby material used in domestic manufacturing is exempt from import duties if the finished product - in this case solar cells used in panels - is then exported.

Polysilicon imports under processing trade rules surged after China imposed duties on purchases from the United States, South Korea and Europe, the Ministry of Commerce said in a statement on its website on Thursday.