When the US government slapped anti-dumping tariffs on China Zhongwang Holdings four years ago, the world’s second-largest producer of aluminium products found solace in China’s booming domestic market.

The company now reports the highest margins of any aluminium producer in the world. But with that status — and major shifts in the market for the lightweight metal — has come fresh global scrutiny. A flood of aluminium pouring out of China and depressing world markets has focused attention on Zhongwang and other Chinese metals processors, whose success threatens to spur new trade tensions with the US.

Late last month, a previously unknown short seller — called Dupré Analytics — accused Zhongwang of routing aluminium through companies controlled by its chairman Liu Zhongtian, allowing it to claim tax rebates from the Chinese government. That metal, it is alleged, is sold at below cost overseas, leading to a build-up of excess aluminium.