BBC newsreaders were forced to put on flak jackets after air raid sirens began sounding in Kyiv.
Lyse Doucet and Clive Myrie were reporting live from the Ukrainian capital as Russian forces invade the country, when the warning interrupted the broadcast.
Sirens have been ringing around the northern city today as people flooded the roads in an attempt to escape.
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It comes as government officials confirmed that the former Soviet republic was seeing a long-anticipated invasion from the east, north and south, with more than 40 soldiers reportedly having been killed and dozens wounded.
"A full-scale war in Europe has begun," Ukrainian presidential adviser Mykhailo Podolyak said.
"Russia is not only attacking Ukraine, but the rules of normal life in the modern world."
Ukraine’s president Volodymyr Zelensky declared martial law and urged citizens not to panic after Russia launched military strikes.
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During an address to the country, he said: "I talked to [US President Joe] Biden, [UK Prime Minister] Johnson, [President of the European Council] Charles Michel, [Polish President Andrzej] Duda, [Lithuanian President Gitanas] Nauseda.
"We started putting together an anti-Putin coalition. I have already urged global leaders to slam Putin with all possible sanctions, offer large-scale defence support and close the airspace over Ukraine for the aggressor. Together we must save Ukraine, save the democratic world, and we will do it."
Mr Zelenskyy also called on people in Russia to speak out against the invasion.
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"To everyone in the Russian Federation who has not lost their conscience, it’s time to come out with protests against the war with Ukraine," he added.
The Ukrainian Minister of Foreign Affairs, Dmytro Kuleba said the country would defend itself against any and all attacks.
He said: "Putin has just launched a full-scale invasion of Ukraine. Peaceful Ukrainian cities are under strikes.
"This is a war of aggression. Ukraine will defend itself and will win.
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"The world can and must stop Putin. The time to act is now."
Since Russian president Vladimir Putin announced the military invasion earlier this morning, terrifying footage has emerged on social media of missile attacks across Ukraine.
A CNN journalist was also forced to try and protect himself following explosions near the capital.
Matthew Chance was reporting on the situation when a series of loud bangs happened right behind him.
He reported that he’d heard ‘a big bang right here behind me’, adding: "There are big explosions taking place in Kyiv right now, I can’t see where they’re taking place from this vantage point here on top of the roof of the hotel in central Kyiv.
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"I can’t explain what they are... I heard four or five explosions moments ago."
Following the attack, Boris Johnson addressed the UK, assuring the country that it was fully behind Ukraine.
He said: "Today in concert with our allies we will agree a massive package of economic sanctions designed in time to hobble the Russian economy."
The PM described the invasion of Ukraine as the 'hideous and barbaric venture of Putin', who - he said - has brought a 'tidal wave of violence' to the country.
Addressing the Ukrainian people, Johnson added: "We’re with you, we’re praying for you and your families.
"I don’t believe the Russian dictator will subdue the national feeling of Ukrainians."
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