In southern China, a zinc smelting factory spilled cadmium, a carcinogenic metal, into the Beijiang River. Millions of people downstream have been warned not to drink tap water.

Xinhua [the official Chinese news agency] reported that local officials were attempting to dilute the levels of cadmium, currently ten times above what is safe, by adding more than 70 million cubic meters of water to the Beijiang River, which joins the Pearl River, one of China's great rivers, further downstream.

Another environmental catastrophe, perhaps even worse, is playing out in northern China. That one began over a month ago when an explosion at a chemical factory dumped 100 tonnes of benzene into the Songhua River. The resultant chemical slick poisoned the water supply for 4 million Chinese in Harbin, northern China. The slick, now 190 kilometres long, has moved into the Amur River that flows north into Siberia, Russia. The 600,000 inhabitants of Khabarovsk, Russia, have been warned that, as a result of the chemical spill in China a month ago, their water supply and central heating will be shut off imminently. The weather forecast for Khabarovsk calls for temperatures around -30C (-22F).

Last night 3,000 Chinese labourers were racing to complete a sandbag dam to protect the city’s 600,000 people and prevent the environmental disaster from souring relations between Moscow and Beijing. Russian military helicopters dropped a disused railway carriage into the river to try and complete the 300m dam.

Water experts said it would not stop the slick, which is 120 miles (190km) long, contaminating water supplies for up to a million Russians and causing long-term ecological damage.

In Khabarovsk, residents have been stockpiling drinking water and food to sustain them until the slick passes in about a week.

Fishing in the region may be banned for as long as four years — a huge blow to 23,000 people in fish-eating communities along the Amur.

The latest news is that the slick passed the city limits just before nightfall this evening.

Authorities estimate it could be at least four days before all of the spill passes through Khabarovsk. However, experts say the effects could last much longer than that. Benzene is heavier than water and there are concerns that it will cling to the riverbed. There are also fears that when the ice melts in the spring, the chemicals will pollute the riverbank.

Although the disaster is fueling anti-Chinese sentiment in eastern Siberia, Moscow is being advised to focus instead on economic opportunities presented by Chinese industrial development.