Workers successfully dammed a waterway in the Heilongjiang River, northeast China, yesterday morning before a toxic slick caused by a chemical spill reached a Russian city downstream.

The 443-meter dam is 4 meters high and about 3 kilometers from Fuyuan waterway, linking the Heilongjiang River and Wusuli River, that supplies water to Russia's eastern city of Khabarovsk, according to officials with the construction headquarters at the site.

"With the dam, the toxic slick will steer clear of Khabarovsk's water intake in the lower reaches of the Fuyuan waterway, ensuring safe water in the city," said Meng Wei, head of the Chinese Research Academy of Environmental Science, at the site.

The slick was expected to reach Khabarovsk yesterday or today, Russia's Emergency Situations Ministry said.

The chemical spill in the Songhua River, a tributary of the Heilongjiang River, was caused by a blast at a Chinese petrochemical plant in November in Jilin Province.

It is estimated about 100 tons of benzene spewed into the river.

Work to dam the waterway began last Friday. About 4,000 workers and 400 vehicles were mobilized. By the time the dam was completed at 11:38am yesterday, about 930,000 cubic meters of earth and stone had been thrown into the river, said authorities.

At the request of the Russians, the two countries agreed to build the temporary dam, which would be removed after the pollutant slick passes Khabarovsk.

China will pay for the construction and demolition of the dam, said Zhang Zuoji, governor of Heilongjiang Province, at the site.

Workers were reinforcing the dam and Chinese and Russian experts were jointly monitoring the river's water quality.

After the chemical spill, China has provided Russia with water testing and purifying materials to help it deal with the water pollution.

China's State Environmental Protection Administration has launched a program to appraise and monitor the ecological impact of the chemical spill.

SEPA has also mapped out a water quality appraisal plan for next spring to ensure the safety of drinking water when ice melts in the Songhua River.