A Maxar satellite image shows the bombed out Mariupol theater.

Lviv, Ukraine (CNN) When Serhii woke up to news reports that a bomb had flattened Mariupol’s Drama Theater, where hundreds of people had been sheltering, he couldn’t breathe.

His wife and their two daughters were inside.

A day before the attack, the 56-year-old editor, who lives in the Ukrainian capital Kyiv, received a panicked call from his 30-year-old daughter.

He hadn’t heard from her since March 1, when Russian forces intensified their siege of Mariupol, the strategic port city, launching a relentless barrage of rockets and bombs from land, sky and sea.

As electricity and internet service went out, Mariupol was largely cut off from the outside world. Serhii, who asked that only his first name be used for security reasons, waited desperately for any update from his girls.

In its absence, he had little choice but to rely on the grim picture of life and death being relayed by Mariupol officials: Residents were living in “medieval conditions,” forced to melt snow for water and cook food outside on open fires. Civilian targets, including apartment buildings, a maternity hospital and the main administrative building, were reduced to rubble. Ceasefires were ignored and evacuation corridors blocked.

The Russian word ДЕТИ, or "Children," is seen on the grounds of  Mariupol's Drama Theater prior to being bombed.

It was a situation that would have been unthinkable a few short weeks ago in the bustling industrial city, once known for its seaside resorts and a major steel plant, and now the scene of fierce fighting between Russian and Ukrainian forces.

Serhii worried for his wife, 56, and daughters — especially the eldest, 36, who lives with a disability and needs daily medication. But his relief at finally hearing from them was quickly replaced by a gnawing fear.

In a harried conversation, his youngest told him she had been able to charge her phone at a diesel generator, but that she only had a little time to talk. She explained that their apartment had been destroyed in the shelling, and she wasn’t sure where they would be safe. He told her to go to the Drama Theater, in the city center, where officials were organizing buses to evacuate residents.

“When I advised them to move to the drama theater as an evacuation site, and the next morning I learned that this place was bombed … I almost went crazy, insane,” Serhii told CNN in a phone call from Kyiv. “Because I actually sent them under the bombs.”

The March 16 bombing of Mariupol’s theater, where Ukrainian officials say an estimated 1,300 had sought refuge, was among the most brazen of Russia’s attacks on civilians since its invasion began in late February. Painted on the ground outside the building — in giant Cyrillic letters — was the word “CHILDREN.” The message — large enough to be viewed from the sky — was scrawled near a public square that, before the war, was busy in summer with kids swinging on a jungle-gym and running through fountains. Russia has denied its forces hit the theater, claiming instead that the Azov battalion, the Ukrainian army’s main presence in Mariupol, blew up the building.

“When I advised them to move to the drama theater as an evacuation site, and the next morning I learned that this place was bombed … I almost went crazy, insane. Because I actually sent them under the bombs.”

Serhii

After 24 hours of near-hysteria, wondering if his family was still alive, Serhii’s phone rang. His daughter told him she had left the theater to check on an elderly relative shortly before the bomb struck. She rushed back to find the building cleaved in half, with the central auditorium of 600 to 800 seats completely flattened, and people drenched in blood and white debris beginning to emerge from the rubble. Among them were her sister, who had been hiding in a portion of the theater that did not collapse, and her mother, who was dug out of the bomb shelter along with other survivors.

The three women, carrying nothing but a backpack with their essential documents, managed to catch a ride with six others in a small car, paying the driver all the money they had — 2,000 hryvnia, the equivalent of about $68. She said they got out at a checkpoint manned by Russian soldiers, and walked some 12 miles further on to Melekino, where their neighbors have a dacha, or summer house.

The small village on the Sea of Azov is overflowing with displaced people who have poured in from Mariupol, Serhii’s daughter told him, adding that there was no food or fuel left.

“In Melekino there is a real famine, a holodomor. People in the villages have no supplies, absolutely all shops are closed,” Serhii said, referring to the man-made famine that gripped the Soviet republic of Ukraine in the early 1930s, killing millions. The term is derived from the Ukrainian words for hunger (holod) and extermination (mor).

Mariupol residents cooking what food they could find outside their homes.

Unable to travel himself, Serhii is now frantically searching for a driver who will make the dangerous journey to retrieve his wife and daughters from the dacha where they’re camping out. But he hasn’t had any luck yet. It’s a frightening proposition: any volunteer would run the risk of being caught in the crossfire, or being captured by the Russians. Over the last week, Russian forces have been deporting thousands of Mariupol residents against their will to far-flung cities in Russia, according to city officials and witnesses. And on Monday, Moscow called on Mariupol to surrender — a notion Ukraine swiftly shot down.

Serhii’s family’s harrowing escape from Mariupol is among the first stories to surface from survivors of the theater bombing. For days, family and friends of those inside have waited on tenterhooks for news of their fate, posting in local Telegram channels and Facebook groups asking if anyone has seen their loved ones. Posts from some of those who have managed to escape the city haven’t instilled much hope, describing basements turned into tombs, and streets littered with dead bodies.

Petro Andriushchenko, an adviser to Mariupol’s mayor, told CNN on Sunday that the battle for the city has made it impossible to retrieve and identify the dead, or treat the wounded. “We cannot carry out rescue operations in the current conditions: Street fighting, shelling, bombing are going on,” he said of the theater attack, adding that many of the estimated 200 survivors are now in other shelters, or in the process of being evacuated to Zaporizhzhia, a city on the Dnieper River about 140 miles away.

Buildings and cars destroyed in the bombardment of Mariupol.

On Sunday, another strike hit an art school in the city, where Andriushchenko said 400 people were believed to be sheltering. But with fierce fighting and communications down, it has been difficult to get a clear sense of the loss of life there.

In a video message posted to Facebook in the early hours of Sunday, Ukrainian President Volodymyr Zelensky said the siege of Mariupol would go down in history as a war crime. “To do this to a peaceful city … is a terror that will be remembered for centuries to come,” he added.

But like the other cities and towns dotted across Ukraine’s east and south which are now being strangled by Russian troops, Mariupol has become a black box, with information only beginning to trickle out as residents escape.

‘I realized that I could wait no longer.’ We had to leave.

After the maternity hospital near Anna Kotelnikova’s home was hit on March 9, sending pregnant mothers scrambling through the ruins clutching their bellies, she decided to move to her parents’ apartment six miles south, in a block overlooking the Drama Theater.

Kotelnikova, a 36-year-old anaesthesiologist, has volunteered as a medic for the Ukrainian army since the spring of 2014, when Russia-backed separatists attacked Mariupol; separatist forces held the city for a month before the Ukrainian government wrested back control. Because of her involvement in the conflict, Kotelnikova was strongly advised to leave Mariupol when Russia invaded Ukraine last month. She refused, unable to conceive of the carnage that was in store for her beloved hometown.

But as the bombing worsened, the barrage increasingly unpredictable and indiscriminate, she began to change her mind. On the night of March 14, sheltering with her sister, brother-in-law, nephew and her parents — who are in their 80s and lived through Mariupol’s occupation by Nazi Germany — she knew they had to leave.

A photo taken outside the Drama Theater before it was bombed, where people were burning branches and debris to keep warm.

“Every day we heard explosions approaching, bombing. That night was just awful. From midnight until the morning … The bombing did not stop,” she told CNN in a call. “When it was possible to open the curtain … I saw that everything in the direction of my house was in black smoke.”

“I realized that I could wait no longer,” she said.

Across the square from her parents’ apartment, locals and city officials were organizing evacuations at the Drama Theater. Inside, the situation was dire, Kateryna Erskaya, a journalist who had been delivering aid to the site, told CNN.