The disaster has strained China's relations with Russia, where authorities in a city downstream from the disaster complain that Chinese officials haven't told them enough about the poisonous benzene headed their way.
The Songhua flows into the Heilong River, which crosses the border and becomes the Amur in Russia, flowing through the city of Khabarovsk.
Russian environmental officials played down the threat on Friday, but regional authorities prepared contingency plans including a shutdown of water systems in cities that drink from the river.
A UN environmental agency says it has offered to help China with the spill but has received no response.
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