Sergei Shoigu told journalists in Novosibirsk that the contaminants may have entered Russia's Amur River on 28 November already. Earlier estimates indicated it would take more than a week for the toxic slick to arrive in Russia via China's Songhua River.
The Songhua was coated with a 100-kilometer-long toxic slick after an explosion on 13 November at a Chinese chemical plant spilled poisonous nitro-benzene into the river near the city of Harbin.
Officials from Russia's Emergency Situations Ministry say drinking water and filtering charcoal are being stockpiled in the Far Eastern city of Khabarovsk.
The spill has the potential to affect 70 Russian cities and villages with a total of over 1 million residents along the Amur.