A week after scrambling to handle a discharge of tonnes of poisonous metals into a local river on which millions rely for drinking water, Jiang Yimin, the chief of the environment protection bureau in Hunan, south-central China, was adamant. Further spillages would be prevented, he vowed to visitors.

In Mr Jiang's sights were 50 to 60 small factories producing indium, a metallic element used in the manufacture of semi-conductors and liquid-crystal display screens, near the Xiang river, about an hour by road from the provincial capital, Changsha. "I am signing the order to close them today!" he declared.

Moments later, however, Mr Jiang's assistant phoned the local environmental officials to request they show visitors the bureau's work in the area, only to be rebuffed. Permission would have to come from the county government first. It was a telling reminder that the authority of even senior officials such as Mr Jiang means little on the ground.

Once upon a time China's environmental problems would scarcely have mattered beyond its borders. But the country's high-speed growth and energy-intensive development model, combined with ineffective local enforcement of anti-pollution rules, has transformed its national shortcomings into a global problem.