Updated

Survivors have begun to emerge from the basement shelter of a Ukraine theater targeted by Russian airstrikes in the besieged city of Mariupol, as casualties throughout the country mount. 

The airstrikes from Wednesday night had left a large section of the grand, 3-three story theater building in the center of Mariupol collapsed in a smoking ruin, according to photos released by the city council. Inside, hundreds of men, women and children — up to 1,000 according to some officials — had taken shelter in the basement, seeking safety amid Russia's strangulating 3-week siege of the strategic southern port city.

Rescuers worked to clear the rubble that had blocked the entrance to the basement, despite new strikes reported elsewhere in the city Thursday. Miraculously, the shelter stood firm, officials said. 

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"The building withstood the impact of a high-powered air bomb and protected the lives of people hiding in the bomb shelter," Ukraine’s ombudswoman Ludmyla Denisova said on the Telegram messaging app Thursday.

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She and Ukrainian parliament member Sergiy Taruta said some survivors had emerged. "People are coming out alive," Taruta wrote on Facebook, though he did not say how many.

It was not known if there were injuries or deaths among those inside.

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The United Nations Human Rights Office of the High Commissioner reported that as of Wednesday, 726 people had been killed, including 674 adults and 52 children. Meanwhile, 1,174 people were injured, including 63 kids, the office said. 

WARNING: THE FOLLOWING CONTAINS GRAPHIC IMAGES 

The Associated Press contributed to this report.