Russia has launched war on Ukraine, firing missiles on cities and destroying military targets, after Russian President Vladimir Putin declared a military operation in a pre-dawn television address on Thursday.
The invasion by land, air and sea is the biggest attack on a European state since the Second World War.
Ukrainian authorities have reported troops pouring across Ukraine's borders from Russia and Belarus to the north and east and landing on the southern coasts from the Black Sea and Azov Sea.
Ukraine has declared martial law and severed all diplomatic relations with Russia.
Ukrainian President Volodymyr Zelenskyy has called on Ukrainians to defend their country and said arms would be given to anyone who wants them.
Russia's military action has prompted widespread international condemnation, including from Australian Prime Minister Scott Morrison, US President Joe Biden, British Prime Minister Boris Johnson and United Nations Secretary-General António Guterres.
How did it come to this?
Thursday’s invasion followed weeks of military build-up and diplomatic efforts by Western leaders to avert war.
Recent tensions between the countries have been simmering since Russia mobilised more than 100,000 troops on its border with Ukraine in November 2021.
The military escalation had prompted nations to warn Russia of sweeping Western economic sanctions if it invaded Ukraine.
Why are Russian troops being sent to Ukraine?
In a televised address on February 24, Mr Putin said he had ordered a "special military operation" to protect Russian-speaking residents in the Donbas region of eastern Ukraine, which he claims are being subjected to "genocide" - an accusation refuted by UN Secretary-General Antonio Guterres.
The Russian president justified the invasion, saying attempts to avoid violence failed.
"Everything that's going on is a least-evil solution. They created such security risks that we couldn't react otherwise. All our attempts failed. To be honest, I'm even surprised by what's occurred," Mr Putin said.
However, US President Joe Biden said Vladimir Putin's agenda has always been larger.
“He has much larger ambitions than Ukraine. He wants to in fact re-establish the former Soviet Union. That's what this is about,” Mr Biden said.
Mr Putin denied for months that he was planning an invasion and has threatened other countries trying to intervene with “consequences you have never seen”.
The Ukraine president Volodymyr Zelenskyy has activated Ukraine forces including drafting reservists aged 18 to 60 and vowing to arm citizens willing to fight.
“Russia treacherously attacked our state in the morning, as Nazi Germany did in the WW2 years,” the Ukraine president tweeted.
He also called on Russian citizens to stand against the military invasion.
“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.”
Russian police have detained more than 1,700 people at anti-war protests across dozens of Russian cities as thousands took to the streets denouncing the Kremlin's attack on Ukraine.
What’s the political context in the region?
A democratic nation of 44 million people, Ukraine is Europe's second largest country by area after Russia.
Tensions between the countries date back to 1991 when Ukraine split from the Union of Soviet Socialist Republics (USSR) and gained independence.
A key source of the recent friction has been Ukraine’s desire to join NATO, with Mr Putin campaigning for guarantees that Ukraine would be permanently barred from joining the transatlantic security alliance.
The Russian president had also called on NATO to cease military activity in Eastern Europe.
In 2014, Ukraine’s pro-Russia president Viktor Yanukovych was ousted from office after he refused to sign an EU association agreement, citing pressure from the Russian government to place distance between the EU and Ukraine.
After Mr Yanukovych fled Ukraine as civilians revolted against his government, Russia annexed Crimea, a southern province of Ukraine.
Marko Pavlyshyn, emeritus professor in Ukrainian Studies at Monash University, told that, “Russia has been pressuring Ukraine in many ways that are designed to destabilise it, divide it and make its democratic project appear unviable.”
The conflict between Russia and pro-Russian forces on the one hand, and Ukraine on the other, has been ongoing since 2014, and resulted in the displacement of up to 1.5 million Ukrainians, according to the United Nations.
What’s Australia’s position?
Speaking on Thursday, Mr Morrison denounced Russia’s "unprovoked" military escalation as a breach of international law.
The prime minister said Australia is not intending to send troops to Ukraine, adding there has been no formal request for that type of help.
He also repeated advice urging more than a thousand Australians still located in Ukraine to leave where safe to do so.
The Australian Government will also impose additional sanctions against members of Mr Putin's inner circle, the prime minister declaring there must be a cost to what he describes as their "reprehensible violence".
Opposition Leader Anthony Albanese said all Australians stood with the people of Ukraine “united in condemnation of Russia’s shameful act of aggression”.
Amid the crisis, the Australian government has promised visa applications from Ukrainian nationals are being fast-tracked for processing.
The government said it will expedite 430 outstanding applications from Ukrainian citizens to come to Australia, across a range of visa classes and that those with visa’s expiring up to June 30 will be granted a six-month extension.
What are the reactions of Australia’s Ukrainian and Russian communities?
Members of Australia’s Ukrainian community have expressed over Russia's invasion of Ukraine.
Stefan Romaniw, Australian Federation of Ukrainian Organisations co-chairman, said there is a need for decisive action to support Ukrainians abroad.
In communities around Australia people have demonstrated their support for peace in Ukraine, at rallies, vigils and church services.
Members of the Ukrainian community described their fear for loved ones.
“I immediately called my parents, woke them up so that they could get ready to leave, prepare some things and documents or try to hide,” one Ukrainian-Australian resident told SBS.
“It’s scary when my sister, a small child, speaks on the phone that they hear explosions, hear sirens... A child shouldn't go through this, and no human should.”
“My dad and uncle can't leave the territory of Ukraine. I don't even know if I'll ever be able to see them again".
While many members of the Russian community have also thrown their support behind calls to withdraw Russian forces.
Alevtina, a Russian-Australian resident attended a Sydney protest in her evening dress.
She says she flew in from Queensland for a friend’s wedding, but she couldn't help but go to the protest first.
Alevtina, a Russian-Australian resident attended a Sydney protest in her evening dress. Source: SBS News
“I'm here today to say that I love Russia very much, but I'm against the current regime.
“In many Russian cities people took to the streets yesterday, despite arrests and beatings, to say no to war.”