Russian President Vladimir Putin announces a "military operation" in Ukraine's Donbas region, BBC reports.
He urges Ukrainian soldiers in eastern Ukraine to lay down weapons and return to their homes.
Putin warns that Moscow's response will be "instant" if anyone tries to take on Russia.
Ukraine's foreign minister accuses Russia of starting a full-scale war, and urges the UN "to do everything possible" to stop it.
US President Joe Biden vows that the world will hold Russia accountable, predicting major loss of life.
Biden will address Americans on Thursday about the consequences he says Russia will face.
Nato chief Jens Stoltenberg says the bloc stands with Ukraine at this terrible time, and will do all it takes to defend all allies.
Ukraine's President Volodymyr Zelensky earlier said an invasion "could be the beginning of a big war on the European continent".
In a late-night address to the nation, he had vowed "we will defend ourselves" in the event of an attack.
Ukraine entered a month-long state of emergency at midnight on Thursday local time (22:00 GMT).
Source: BBC
BDST: 1236 HRS, FEB 24, 2022
SMS