Russia says it feels a 'constant threat from the territory of modern Ukraine' as it sent missiles and troops into the country sending shockwaves around the world.
Russian forces fired missiles at several cities in Ukraine and landed troops on its coast on Thursday, officials and media said, after President Vladimir Putin authorised what he called a special military operation in the east.
Shortly after Putin spoke in a televised address on Russian state TV, explosions could be heard in the pre-dawn quiet of the Ukrainian capital of Kyiv.
Putin said Russia did not plan to occupy Ukrainian territory.
"I urge you to immediately lay down your weapons and go home. All servicemen of the Ukrainian army who fulfil this demand will be able to freely leave the combat zone and return to their families.
"Russia cannot feel safe, develop, and exist with a constant threat emanating from the territory of modern Ukraine.
"All responsibility for bloodshed will be on the conscience of the ruling regime in Ukraine."
The United States and other United Nations Security Council members slammed Russian President Vladimir Putin for attacking Ukraine as the 15-member body met in New York to try and defuse weeks of mounting tensions.
Russia's UN Ambassador Vassily Nebenzia notified the council of Moscow's move during the meeting, justifying it under Article 51 of the UN Charter, which covers individual or collective self-defence by states against armed attack.
Ukraine's UN Ambassador Sergiy Kyslytsya said Russia had just declared a war on his country and told Nebenzia at the end of the council meeting: "There is no purgatory for war criminals. They go straight to hell."
Nebenzia responded: "We aren't being aggressive against the Ukrainian people, but against the junta that is in power in Kyiv."
Russia has suspended movement of commercial vessels in the Azov sea until further notice, five grain industry sources told Reuters on Thursday.
Russia, the world's largest wheat exporter, mainly ships its grain from ports in the Black Sea.
Russian troops attacked Ukraine from Belarus as well as Russia with Belarusian support at about 5am local time on Thursday, and an attack was also being launched from annexed Crimea, Ukraine's border guard service said.
Ukrainian Foreign Minister Dmytro Kuleba 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. The world can and must stop Putin. The time to act is now."
Ukranian President Volodymyr Zelensky has declared martial law as the country prepares to resist the Russian invasion.
Zelensky urged Ukranians not to panic, saying they were ready for anything and would emerge victorious. He told citizens to stay at home, to avoid air strikes.
Here's how world leaders responded to Russia's invasion of Ukraine
In a statement, New Zealand Foreign Minister Nanaia Mahuta said Aotearoa "unequivocally condemns this unprovoked and unjustified attack" and stands with the people of Ukraine.
"Russia's actions are a flagrant breach of fundamental international rules; the use of force to change borders is strictly prohibited under international law.
"We join the international community in calling on Russia to cease military operations in Ukraine, and immediately and permanently withdraw, to ensure all possible steps are taken to protect civilians in line with international humanitarian law, and return to diplomatic negotiations to de-escalate this conflict."
Australian Prime Minister Scott Morrison said Russia had launched a "brutal" and illegal invasion of Ukraine that would be met with a severe response by Australia and the international community.
"I will call it what it is: the Russian government launched a brutal invasion, unprovoked, on Ukraine and should be condemned for doing so," Morrison said.
US President Joe Biden, who has ruled out putting US troops on the ground in Ukraine, said Putin had chosen a premeditated war that would bring a catastrophic loss of life and human suffering.
"Russia alone is responsible for the death and destruction this attack will bring, and the United States and its allies and partners will respond in a united and decisive way," he said.
UK Prime Minister Boris Johnson on Twitter said: "I am appalled by the horrific events in Ukraine and I have spoken to President Zelenskyy to discuss next steps.
"President Putin has chosen a path of bloodshed and destruction by launching this unprovoked attack on Ukraine. The UK and our allies will respond decisively."
"We must immediately respond to Russia's criminal aggression on Ukraine. Europe and the free world has to stop Putin. Today's European Council should approve fiercest possible sanctions," Polish Prime Minister Mateusz Morawiecki said.
Czech Prime Minister Petr Fiala said on Twitter that the Russian invasion of Ukraine was an "absolutely unjustifiable act of aggression toward and independent country, which cannot remain without reaction from EU and Nato."
Romanian President Klaus Iohannis also condemned the Russia attack calling it a "very grave breach of international law, of Ukraine's sovereignty and integrity."
"I strongly condemn Russia's military aggression against Ukraine. This act undermines the sovereignty and independence of Ukraine and constitutes a grave breach of international law," Bulgarian Foreign Minister Teodora Genchovska said on Twitter.
Norway, a Nato member that shares a border with Russia in the Arctic, condemned Russia's attack on Ukraine. "Russia has the full and whole responsibility for throwing Europe into this very dark situation," Prime Minister Jonas Gahr Stoere said.
Separately, the Norwegian foreign ministry said it was moving its embassy in Ukraine to the western city of Lviv from the capital, Kyiv.
French President Emmanuel Macron condemned Russia's military actions. "France strongly condemns the decision of Russia to start a war with Ukraine. Russia must immediately put an end to its military operations," wrote Macron on his Twitter account.
Sweden has moved its remaining embassy staff to Lviv from the Ukrainian capital Kyiv, Foreign Minister Ann Linde said on Twitter on Thursday.
"All diplomatic staff relocated to Lviv last night," she said. "Embassy continues to operate from there."
Germany's defence minister said it was never too late for dialogue with Russia while underscoring that Nato and the European Union stood united in the face of Moscow's "drastic breach of international law".
Denmark's foreign ministry said has shut down its embassy in Ukraine capital Kyiv, it said in a notice on its web page on Thursday, citing safety concerns.
South Korean President Moon Jae-in said on Thursday the country will join in imposing economic sanctions on Russia over its military operations in Ukraine, Yonhap news agency reported.
Spanish Prime Minister Pedro Sanchez on Thursday morning condemned the Russian military operation in Ukraine and said he was in contact with allies from Nato to coordinate a response.
Portugal Foreign Minister Augusto Santos Silva called on Thursday for an immediate end of the Russian military operation in Ukraine.
"The military operation launched this morning by Russia on Ukraine's territory is an unjustified aggression and a gross violation of international law," Santos Silva said on his Twitter account.
China's embassy in Kyiv told its citizens in Ukraine to stay home or at least take the precaution of displaying a Chinese flag on their vehicles if they needed to drive anywhere, following Russia's attack on the country.
China has so far stopped short of telling its citizens to consider leaving Ukraine. A security advisory issued by the embassy earlier this week had warned Chinese nationals to stock up on daily necessities such as food and water.
Japanese Prime Minister Fumio Kishida said on Thursday that Japan strongly condemns the one-sided actions of Russia, following reports that Russian forces had fired missiles at several Ukrainian cities.
Kishida said he has instructed the relevant Japanese authorities to do everything possible to ensure the safety of Japanese nationals in Ukraine.
- Reuters / RNZ / ABC / BBC