Russian President Vladimir Putin launched a full-scale invasion of Ukraine on Thursday, killing dozens and forcing hundreds to flee for their lives.
Russian air strikes hit military facilities across the country and ground forces moved in from the north, south and east, triggering condemnation from Western leaders and warnings of massive sanctions.
Weeks of intense diplomacy failed to deter Putin, who massed over 150,000 troops on Ukraine's borders in what the West said was the biggest military build-up in Europe since the Second World War.
"I have decided to proceed with a special military operation," Putin said in a television announcement in the early hours of Thursday.
Shortly afterwards, the first bombardments were heard in Ukraine's capital, Kyiv, and several other cities, according to AFP correspondents.
At least 68 people were killed, including both soldiers and civilians, according to an AFP tally from various Ukrainian official sources.
In the deadliest single strike reported by the authorities, 18 people were killed at a military base near Ukraine's Black Sea port city of Odessa.
Ukraine's border guards said Russian forces had reached the region around the capital, Kyiv.
An AFP reporter in the northern part of the city saw several low-flying helicopters overhead amid reports that an airfield was under attack.
Ukrainian Foreign Minister Dmytro Kuleba said a "full-scale invasion" was underway.
President Volodymyr Zelensky declared martial law and said Russia was attacking his country's "military infrastructure" but urged citizens not to panic and vowed victory.
He accused Russia of acting like "Nazi Germany", saying it had attacked in a "cowardly and suicidal way".
Ukrainian forces said they had killed "around 50 Russian occupiers" while repulsing an attack on a town on the frontline with Moscow-backed rebels, a toll that could not be immediately confirmed by AFP.
- 'Sounds of bombing' -
Kyiv's main international airport was hit in the first bombing of the city since World War II and air raid sirens sounded over the capital at the break of dawn.
"I woke up because of the sounds of bombing. I packed a bag and tried to escape," Maria Kashkoska told AFP, as she sheltered inside the Kyiv metro station.
In the eastern Ukrainian town of Chuguiv, a son wept over the body of his father among the wreckage of a missile strike in a residential district.
"I told him to leave," the man sobbed repeatedly, next to the twisted ruins of a car.
Kuleba said the worst-case scenario was playing out.
"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," he said.
Within a few hours of Putin's speech, Russia's defence ministry said it had neutralised Ukrainian military airbases and its air defence systems.
Ukraine said Russian tanks and heavy equipment crossed the border in several northern regions, in the east as well as from the Kremlin-annexed peninsula of Crimea in the south.
Kremlin spokesman Dmitry Peskov said the operation would last as long as necessary, saying there were "goals that need to be achieved".
"Ideally, Ukraine needs to be liberated and cleansed of Nazis," he told reporters, repeating unfounded claims made by the Kremlin.
- 'Unprovoked and unjustified' -
The fighting roiled global financial markets, with stocks plunging and oil prices soaring past $100.
European wheat prices also hit a record high on expectations of lower supplies as Ukraine and Russia are two of the world's biggest producers.
In his televised address, Putin justified the assault by claiming the government was overseeing a "genocide" in the east of the country.
The Kremlin earlier said the leaders of two separatist territories in eastern Ukraine had asked Moscow for military help against Kyiv after Putin recognised their independence on Monday.
A conflict between the self-proclaimed Donetsk and Lugansk republics and government forces has dragged on since 2014, killing more than 14,000 people.
US President Joe Biden spoke with Zelensky after the Russian assault began to vow US "support" and "assistance".
He condemned the "unprovoked and unjustified attack by Russian military forces," and vowed Russia would be held accountable.
Biden was due to join a virtual meeting of G7 leaders -- Britain, Canada, France, Germany, Italy, Japan and the United States -- on Thursday, likely to result in more sanctions against Russia.
In Brussels, EU foreign policy chief Josep Borrell said Russia faced "unprecedented isolation" and would be hit with the "harshest sanctions" the European Union has ever imposed.
NATO said it would also hold a virtual summit and activate "defence plans" for allied countries.
But NATO chief Jens Stoltenberg said: "We don't have any plans to send NATO troops into Ukraine".
The Russian invasion also rattled eastern NATO members once dominated by Moscow during the Cold War.
Poland called for urgent NATO consultations and said it was preparing for a large influx of refugees, while Lithuania imposed a national state of emergency.
- Drop NATO ambitions -
Ukraine has around 200,000 military personnel, and could boost that with up to 250,000 reservists.
Moscow's total forces are much larger -- around a million active-duty personnel -- and have been modernised and re-armed in recent years.
But Ukraine has received advanced anti-tank weapons and some drones from NATO members. More have been promised as the allies try to deter a Russian attack or at least make it costly.
Russia has long demanded that Ukraine be forbidden from ever joining the NATO alliance and that US troops pull out from Eastern Europe.
Putin this week set out a number of stringent conditions if the West wanted to de-escalate the crisis, saying Ukraine should drop its NATO ambition and become neutral.
"Putin's aim is to end the existence of Ukraine as it was yesterday," said Tatyana Stanovaya, founder of the political consultancy R.Politik Center and a non-resident scholar at the Carnegie Moscow Center.
"It is possible that the east of Ukraine will come under Russian control," she said, adding: "I cannot see anything that would stop Russia now".