China's southern business capital of Guangzhou, just north of Hong Kong, rushed Thursday to ensure water supplies as a toxic spill from a smelter flowed toward the city of 7 million.

It was China's second environmental disaster in a month and came as authorities were trying to minimize the impact of a chemical spill on a northeastern river. That toxic slick disrupted water supplies to millions of people in China and has flowed into Russia.

Guangzhou and the nearby manufacturing center of Foshan were ordered to "start emergency plans to ensure safe drinking water supplies to their residents," the official Xinhua News Agency said. The report didn't say what the cities were told to do.

The area is one of China's most densely populated and is a center for the factories that supply its booming export industries.

The spill into the Bei River north of Guangzhou prompted another city, Shaoguan, to cut running water for eight hours on Tuesday. The Bei flows into the Pearl River, which passes through Guangzhou and empties into the South China Sea west of Hong Kong.

A Guangzhou water department spokeswoman said only one of the city's seven water plants is close enough to the river to be affected. The woman, who responded to a telephone call to the department's press office, would give only her surname, Zheng. Phone calls to the city government and environmental bureau on Thursday morning weren't answered.

The government said the spill from a smelter in Shaoguan pushed up levels of the heavy metal cadmium in the Bei to 10 times acceptable limits.

The disaster came a month after a chemical plant explosion in China's northeast spewed 100 tons of benzene and other toxins into the Songhua River, forcing the major city of Harbin to shut down running water.

In Russia, authorities said the toxic slick could reach Khabarovsk, a city of 580,000 people, as early as Thursday. The city already has shut down running water in some areas as a precaution and warned all residents not to drink tap water.

The twin disasters highlight China's chronic environmental problems and the precarious state of its scarce water supplies.

China has suffered a series of such disasters, from toxic spills in rivers to the release of chlorine and other poison gases. Accidents often are blamed on lack of required safety equipment or officials' refusal to enforce environmental rules that might hurt local businesses.

The accidents are an embarrassment to the government of President Hu Jintao, which has promised to clean up environmental damage from China's 25 years of breakneck economic growth.

The government says China's major rivers are badly polluted with such industrial chemicals. It says millions of people live in areas without adequate supplies of clean drinking water.

On the Bei River, the government has set up 20 stations to monitor water quality, Xinhua said.

In Yingde, a city north of Guangzhou and about 50 miles downstream from Shaoguan, Xinhua said authorities used 15 fire trucks and other vehicles to deliver water to urban areas.

Officials in Yingde were dumping water from a suburban reservoir into the river to dilute the toxins and were building a pipe from the reservoir to bring clean water into the city, Xinhua said.