Russian forces have launched a military assault on neighbouring Ukraine, crossing its borders and bombing military targets near big cities.
In a pre-dawn TV statement Russian President Vladimir Putin said Russia did not plan to occupy Ukraine and demanded that its military lay down their arms.
Moments later, attacks were reported on Ukrainian military targets.
Ukraine said that "Putin has launched a full-scale invasion of Ukraine".
Russian military vehicles were said to have breached the border in a number of places, in the north, south and east, including from Belarus, an long-time Russian ally.
A least seven people are known to have been killed, including civilians, but a Ukrainian presidential adviser said that more than 40 soldiers had died and dozens more were wounded.
Ukrainian President Volodymyr Zelensky announced that martial law was now being imposed across all of Ukraine, and then severed all diplomatic relations with Russia.
"No panic. We're strong. We're ready for anything. We'll defeat everyone, because we are Ukraine," he said in a video statement. Ahead of Russia's attack he had made a last-ditch attempt to avert a conflict, warning that Russia could start "a major war in Europe" and urging Russian citizens to oppose it.
Warning sirens blared across the capital, which has a population of almost three million.