Terrified Ukrainians began a mass exodus Thursday as Russia declared war and started launching missiles — as chilling footage also captured a swarm of helicopters attacking an airport near the capital, Kyiv.

Soon after President Vladimir Putin’s televised declaration just before 6 a.m. local time, Russian missiles started raining down, plunging Europe into a nightmare not seen since the darkest days of World War II.

That included explosions that rocked the 3 million people in the capital, Kyiv, where black smoke was seen gushing from the headquarters of Ukraine’s military intelligence.

Later Thursday, video footage captured the chilling scenes of more than half-a-dozen attack helicopters hovering over the city’s rooftops — with huge plumes of black smoke behind them.

Other clips appeared to capture the same choppers repeatedly firing as they move as well as the sound of regular gunshots.

“Fighting is underway for Gostomel airfield,” armed forces chief Valeriy Zaluzhny said in a message posted on Facebook of the military airbase about 15 miles outside of Kyiv.

CNN’s Matthew Chance also filmed troops at the scene, which is also known as the Antonov airport.

“These troops … are Russian airborne forces,” he said in the clip. “They have taken this airport.”

The siege came after Russian Defense Minister Sergei Shoigu crowed that 74 Ukrainian military facilities — including 11 air bases — had been destroyed in the opening salvo of the war.

Ukraine’s military, meanwhile, had said six Russian planes and one helicopter were shot down amid the ongoing aerial assault. The military also said four Russian tanks were destroyed and 50 troops were killed.

Footage shared online appeared to show one Russian chopper crashing into water, with the pilot parachuting in after it through a thick plume of black smoke.

Russia’s defense ministry only acknowledged the loss of one Su-25 attack jet, putting it down to “pilot error.” 

Russian troops also landed by sea at the port cities of Odessa and Mariupol in the south, and Ukraine reported columns of troops pouring across its borders into the eastern cities of Chernihiv, Kharkiv and Luhansk.

Russian tanks also crossed into Sen’kivka, Ukraine, from Belarus on Thursday, CNN footage showed.

By early Thursday, Ukraine confirmed the deaths of at least 40 of its citizens in the attacks, with dozens injured. CNN quoted a government official who said there were likely already hundreds of casualties.

Images showed Ukrainian citizens bandaged and bloodied from the bombings. An apartment building was struck outside Kharkiv, where more casualties were reported.

As the missiles rained down, Ukrainians desperately tried to flee, with astonishing images showing lines of cars as far as the eye could see choking traffic in Kyiv.

Ukraine’s neighbor Moldova also called for a state of emergency as its president, Maia Sandu, said it expected to “accommodate tens of thousands” of refugees.

Ukrainian airspace was closed to civilian aircraft as the region was considered an active conflict zone. The European Union Aviation Safety Agency issued an alert saying there is a risk of “both intentional targeting and misidentification” of civilian aircraft, later expanding it to also warn against flying over Moldova and Belarus.

Putin announced the operation in a live televised speech early Thursday, threatening countries that attempt to interfere with “consequences they have never seen.”

He claimed Russia was undertaking a “special military operation” to demilitarize and “denazify” the country under the pretense that Russia was defending itself.

Ukraine hit back, however, directly comparing Putin to genocidal maniac Adolf Hitler.

The nation’s official Twitter account posted a cartoon that mocked Putin, showing him as small and child-like as he had his cheek lovingly caressed by the late Nazi leader behind World War II.

“This is not a ‘meme’, but our and your reality right now,” the nation’s official account said.

Ukraine’s President Volodymyr Zelensky also tweeted, “Russia treacherously attacked our state in the morning, as Nazi Germany did in the WW2 years.”

“Russia has embarked on a path of evil, but Ukraine is defending itself & won’t give up its freedom no matter what Moscow thinks,” he wrote.

However, Putin claimed the Kremlin has no intention of occupying the country, placing blame for any potential bloodshed on the Ukrainian “regime.”

International intelligence has long expected the Russian leader to use “false flag” operations to justify its aggression against Ukraine.

Putin had directly addressed Ukraine forces in his remarks, urging them to lay down their arms, according to a translation.

President Biden is expected to address the nation at 12:30 p.m., the White House said, following several other Western leaders who spoke in a series of somber televised addresses earlier Thursday.

The president met with his G7 counterparts at 9 a.m. ET Thursday to announce further sanctions from the US and allies for “this needless act of aggression.”

British Prime Minister Boris Johnson told his nation that “our worst fears have now come true.”

“President Putin has unleashed war in our European continent,” he said in a live televised address, noting that “all our warnings have proved tragically accurate.”

“He has attacked a friendly country without any provocation and without any credible excuse. Missiles and bombs have been raining down on an entirely innocent population.

“Our mission is clear: diplomatically, politically, economically and eventually militarily, this hideous and barbaric venture of Vladimir Putin must end in failure,” Johnson added.

French President Emmanuel Macron called it “the most serious attack on peace and stability in our Europe for decades.”

“We will show no weakness,” he vowed, while acknowledging it was a “turning point in European history” that will have “profound consequences for our continent and changes in our lives.”

China, however, refused to condemn the attack, questioning whether it was even an invasion — and instead blaming the US for “fanning the flame” of tensions.

Amid sanctions from a slew of other nations, China instead approved imports of wheat from all regions of Russia Thursday, ending its ban due to concern about possible fungus and other contamination.

President Biden released a statement shortly after military action began, calling the aggression “an unprovoked and unjustified attack” by Russia.

“Putin has chosen a premeditated war that will bring a catastrophic loss of life and human suffering,” he said in a statement late Wednesday.

“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. The world will hold Russia accountable.”

Dmytro Kuleba, Ukraine’s minister of foreign affairs, said in a statement that Putin had launched “a full-scale war” against Ukraine.

“Strikes continue on peaceful Ukrainian cities,” Kuleba said. “This is a war of aggression. Ukraine will defend and win. The world can and must stop Putin. It’s time to act — just now.”

The invasion follows frantic diplomatic efforts by the US and its Western allies to find a middle ground with Moscow after rejecting the Kremlin’s insistence that Ukraine be kept out of NATO, as well as that the alliance draw back its forces from Eastern Europe and not deploy missile systems inside Ukraine.

US officials estimated that Russia had massed between 150,000 and 190,000 troops along Ukraine’s border in recent months, which one diplomat described last week as “the most significant military mobilization in Europe since the Second World War.”

The situation began deteriorating on Monday after Putin delivered an astonishing speech in which he ranted and raved that Ukraine was not a standalone nation but rather “an integral part” of Russia.

Delivering a distorted history lesson, the Russian leader insisted that “modern Ukraine was entirely created by Russia — more precisely, Bolshevik, Communist Russia” and lamented that Soviet leaders going back to Vladimir Lenin had erred by “giving in to nationalists.”

“Why did we have to be so generous, and then give these republics the right to leave?” the Russian leader asked at one point, making a clear reference to the breakup of the Soviet Union in 1991. “Madness.”

At the conclusion of his speech, Putin recognized two pro-Russian breakaway enclaves in eastern Ukraine as independent states and signed a decree ordering troops to the region to perform “peacekeeping functions.”

The so-called Donetsk People’s Republic and Luhansk People’s Republic broke away from Ukraine after Russian invaded and annexed Crimea in 2014. Fighting has continued ever since with an estimated death toll of more than 14,000.

On Tuesday, Biden denounced Putin’s actions as the “beginning” of an invasion of Ukraine and announced new economic sanctions targeting Russia.

“This is a flagrant violation of international law and demands a firm response from the international community,” Biden said.

Meanwhile, the US also informed the United Nations that its intelligence indicated that Russia was compiling lists of Ukrainian dissidents “to be killed or sent to camps” following an invasion.

With Post wires