Approximately 600 people were in the building when it was attacked, according to Petr Andryuschenko, an advisor to Mariupol’s mayor.
The attack is thought to have resulted in the most deaths in a single strike since the invasion began.
Because communication with Mariupol is still difficult, independent verification of information is challenging.
Russia has denied responsibility for the internationally condemned strike.
The word “children” had been painted in big letters on the ground outside the city’s central theatrical building at the time of the strike.
Following the incident, both Ukrainian Foreign Minister Dmytro Kuleba and the municipal council accused Russia of committing a war crime.
Mothers looking for their children under the rubble, and a five-year-old screaming that he did not want to die, were related by survivors to the BBC.
Before the attack, Mr. Andryuschenko told the BBC’s Newshour that 600 people were inside the building, with roughly 300 of them in a basement bunker.
He said that the officials were able to verify the death toll because the record of who was in the theatre before the missile hit was with them and he spoke with survivors.
Due to Russian shelling nearby, the authorities were unable to begin a rescue mission.
In a telegram post earlier this week, Mariupol municipal hall cited a similar death toll.
Official wrote,”From eyewitnesses, information is emerging that about 300 people died in the Drama Theatre of Mariupol following strikes by a Russian aircraft.
Mr. Andryuschenko also confirmed that battle was still going on in the city’s heart, but stressed that Russian forces had not yet taken control.
Mariupol, the port city of Ukraine, is crucial for Russia’s military campaign. If Odesa falls, Russia will gain control of one of Ukraine’s most important ports, as well as a land corridor connecting Crimea to the Russian-backed regions of Luhansk and Donetsk.
As written by Hugo Bachega of the BBC, the catastrophe of Mariupol’s theatre will be remembered as an unjustified and most likely planned attack on civilians. Another horror in a city has seen a lot of them throughout the conflict.
The location, a massive Soviet-era structure in the heart of the city, had been identified as a civilian refuge, with the word “children” inscribed in Russian on the ground outside. He said that the attack could not be unintentional and unplanned.
Hundreds of civilians had gone there, mostly women, children, and the elderly escaping homes that were no longer safe or standing. They believed it would provide them with some level of protection.
In Mariupol, however, such a site does not exist. The majority of the city is in ruins, street after street, and building after building. Thousands of people are still trapped within, facing a siege akin to that of the Middle Ages. Food and water were scarce, as well as electricity and gas.
Russia is accused of attempting to starve the city to death. Mariupol, despite its suffering, vows it will not succumb for the time being.