Russian President Vladimir Putin says his aim is to demilitarise and 'denazify' Ukraine.
Missiles rained down on Ukrainian cities and explosions were heard near the capital Kyiv. Ukraine's military said it destroyed four Russian tanks near the eastern city of Kharkiv, killed 50 troops in the Luhansk region and downed a sixth Russian aircraft.
Ukrainian President Volodymyr Zelensky urged all citizens prepared to defend the country to come forward, saying Kyiv would issue weapons to everyone who wants them.
Central European countries have started preparations to receive people fleeing Ukraine.
Ukraine has closed its airspace to civilian flights.
Photo credit: Getty Images Caption: Firefighters work on a fire on a building after bombings on the eastern Ukraine town of Chuguiv.