Around 300 Ukrainian civilians were killed in the blown-up Mariupol theater that was being used as a shelter and was clearly marked “CHILDREN,” local officials announced Friday, as a newly released video also gave a harrowing glimpse of the carnage.

“Unfortunately, we start this day with bad news. Eyewitnesses reported that about 300 people died in the Mariupol Drama Theater,” the council in Ukraine’s hardest-hit city wrote on Telegram of the March 16 bombing.

“I do not want to believe in this horror … I want to believe that everyone managed to escape,” the post’s author wrote.

“But the words of those who were inside the building at the time of this terrorist act say the opposite.”

Soon after the airstrike, Ludmyla Denisova, the Ukrainian Parliament’s human rights commissioner, said more than 1,300 people had been sheltering in the building.

While 130 survivors were reported to have escaped, many were feared trapped in a bomb shelter under the rubble, with rescue efforts thwarted by ongoing shellings, the council had said.

On Friday, video emerged showing dozens of dust-covered people staggering down stairs and through the wreckage of a still-standing section of the theater.

Another clip showed a giant gap where part was instead razed, leaving nothing but crushed timber and debris as a panicked-sounding man said that a lot of people had been hiding there at the time.

It was not immediately clear whether emergency workers had finished searching the site or how eyewitnesses arrived at the horrific death toll.

The council insisted that invading forces deliberately targeted the theater, which had been profiled in media reports because of its role as a makeshift shelter.

Russian bombers “knew what the consequences might be, and yet the bombs fell on a place that had become a refuge for hundreds of Mariupol residents,” the council wrote.

“These fascists of the 21st century were not stopped by the huge inscription CHILDREN, or the statements of the people themselves that there are only peaceful — women, children, the elderly,” the post said.

“There can be no explanation for this inhuman cruelty. There will never be forgiveness for those who brought destruction, pain and suffering to our home.

“We will be able to restore the buildings, but we will never get back friends, neighbors, family and loved ones,” the official body wrote.

The pulverized theater had “always been the city’s calling card,” the council wrote.

“In its place appeared a new point of pain for the people of Mariupol, the ruins that became the last refuge for hundreds of innocent people.”

Mariupol, a city of 430,000, has suffered many of the worst atrocities during the war, leaving it a “freezing hellscape riddled with dead bodies and destroyed buildings,” according to Human Rights Watch.

A week before the theater bombing, a maternity hospital in the city was blown up, killing children and pregnant women.

Both attacks have been blamed on the same top Russian military leader, Col. Gen. Oleksandra Matviichuk — who has been dubbed the “Butcher of Mariupol.”