"The pollution will have negative impact not only on the Khabarovsk region, but also most likely Sakhalin, the Kurils, Hokkaido and shores of continental Russia south of the Amur, and Korea," the chief of the region's external economic policy department Alexander Kiryanov said.

That may include persistent components that are likely to spread wide once the Amur washes them into the sea and which may thus reach humans, as "some toxic materials cannot be flushed out of the human body," Kiryanov warned.

One hundred tonnes of the carcinogens benzene and nitrobenzene were released into the Songhua after an explosion in November 13 at a PetroChina chemical factory in the northeastern province of Jilin.

The spill caused an 80-kilometer-long (50-mile-long) toxic slick to flow down the Songhua, the source of water for millions including the residents of Harbin city, who had their water supplies cut off for days.

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