Several Russian infantry units are reportedly approaching the capital, Kyiv, from the north, south and east of Ukraine.
Ukrainian forces have reportedly been paralyzed by Russian airstrikes and naval strikes.
Ukrainian authorities say Russian forces have taken control of the Chernobyl nuclear power plant in Ukraine.
The catastrophe caused by the plant in 1986 is still considered the worst nuclear disaster in human history, and Ukrainian President Volodymyr Selensky has said that such a catastrophe could happen again if Russia continues to invade.
The Ukrainian president also said that he was the first target of the Russian army, and that the second target was his family members, so that he and his family would stay in the capital, Kyiv.