Elizabeth Byrs, spokeswoman for the UN's Office for the Coordination of Humanitarian Affairs, said today that neither country had asked for help so far.
But Byrs said the UN is ready to send experts if needed.
Earlier, officials in the Khabarovsk region in Russia's Far East said they would declare a state of emergency when the 80-kilometer slick of chemicals reaches the Russian border from China.
China says the chemicals from a factory explosion are due to reach the border within two weeks. But there are concerns in Russia the slick could arrive sooner.
Chinese officials yesterday confirmed the slick had reached its northeastern city of Harbin, where 3.8 million people are without tap water.