The emergency services helicopter came down in Brovary, an eastern suburb of the Ukrainian capital Kyiv, killing nine people on board and at least five on the ground.
Interior Minister Denys Monastyrskyi, his deputy Yevhen Yenin, and State Secretary of the Ministry of Internal Affairs Yurii Lubkovych were among the dead, said the chief of Ukraine’s National Police.
Mr Monastyrsky is the most senior Ukrainian official to have died since Vladimir Putin launched his invasion 11 months ago.
The minister had been travelling to a war “hot spot” when the helicopter went down, the deputy head of Ukraine’s presidential office reportedly told the BBC.
Ukraine’s State Emergency Service said on Wednesday afternoon that 14 people were killed in the crash, including nine people who were aboard the helicopter and one child on the ground.
It said 25 people were also injured, including 11 children.
Early official reports placed the death toll and casualty figure higher, but this information was later revised.
Glib, a 17-year-old local resident, told reporters at the scene: “We saw wounded people, we saw children. There was a lot of fog here, everything was strewn all around.
“We could hear screams, we ran towards them. We took the children and passed them over the fence, away from the nursery as it was on fire, especially the second floor.”
Photos from the scene showed debris including broken glass was scattered over a muddy playground. The entire side of the nursery building - which was reportedly packed with children when the tragedy happened - was left charred.
Emergency workers were pictured standing by the mangled wreckage of the helicopter, which appeared to have crushed at least one car.
Video footage captured in the immediate aftermath of the disaster appeared to show a significant area of building ablaze.
There was no immediate word on whether the crash was an accident or a result of the war with Russia. No fighting has been reported recently in the Kyiv area.
“For now, we are considering all possible versions of the helicopter crash accident,” Ukraine’s prosecutor general, Andriy Kostin, said on social media platform Telegram.
An investigation is being carried out by the Security Service of Ukraine, he said.
Ukraine’s first lady Olena Zelenska was seen daubing teary eyes and pinching her nose in emotion minutes before attending a World Economic Forum session in Davos, Switzerland, after news of the tragedy broke.
“Another very sad day today - new losses,” she said.
Forum President Borge Brende requested 15 seconds of silence after opening the session to honour the Ukrainian officials killed in the crash.
In London, Home Secretary Suella Braverman paid tribute to her Ukrainian counterpart Mr Monastyrsky on Twitter, where she said Ukraine had lost a “leading light” in its resistance against Vladimir Putin.
“This is truly heart-breaking. Interior Minister, Denys Monastyrsky was a leading light in supporting the Ukrainian people during Putin’s illegal invasion and when we spoke in October I was struck by his determination, optimism and patriotism,” she wrote.
“My thoughts go out to all those who have died in this horrible tragedy and their families. The UK will always stand with our Ukrainian friends.”
Britain’s ambassador to Ukraine Dame Melinda Simmons tweeted: “Shocked at the tragic death of leadership of @MVS_UA as well as civilians, following a helicoper crash in Brovary.
“I knew well both Minister Monastyrsky & his First Deputy Yenin. My sincere condolences to their families and our Ukrainian government partners over this loss.”
Foreign Secretary James Cleverly described Mr Monastyrsky as “a true friend of the UK”, adding: “We are ready to support Ukraine in whatever way we can.”
The crash came just four days after a Russian missile strike on an apartment building in southeastern Ukraine killed 45 civilians, including six children - marking the deadliest attack on civilians since the spring.
“Haven’t had time to recover from one tragedy, there is already another one,” said the deputy head of the Ukrainian presidential office Kyrylo Tymoshenko.