Survivors began to emerge on Thursday as authorities worked to rescue hundreds of civilians trapped in the basement of a theare blasted by Russian airstrikes in the besieged city of Mariupol, while ferocious Russian bombardment killed dozens in a northern city over the past day, the local governor said.

The strikes the previous evening 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 clearing 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.

“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.

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. Another lawmaker, Lesia Vasylenko, who was in London in a delegation visiting Parliament Thursday, said there were reports of injuries but no deaths.

At least as recently as Monday, huge white letters on the pavement in front of and behind the theater spelled out “CHILDREN” in Russian to alert warplanes of those inside, according to images released by the Maxar space technology company. The Russian defense ministry denied bombing the theater or anywhere else in Mariupol on Wednesday.

The strike against the theater was part of a furious bombardment of civilian targets in multiple cities over past day.

Also struck in Mariupol on Wednesday was a municipal pool where pregnant women and women with children were taking shelter, according to Pavlo Kyrylenko, head of the Donetsk regional administration. Hours later, there was no word on casualties in that strike.

To the north, at least 53 people were brought to morgues over the past 24 hours in the city of Chernihiv, killed amid heavy Russian airtrikes, artillery bombardment and ground fire, the local governor Viacheslav Chaus told Ukrainian TV on Thursday.

Ten people were killed while lining up for bread in the city, the Ukrainian General Prosecutor's Office said Wednesday. Russia has denied involvement.

Chaus said civilians were hiding in basements and shelters without access to utilities in the city of 280,000 people.

“The city has never known such nightmarish, colossal losses and destruction,” he said.

Chernihiv, which is near the borders with Belarus and Russia, was among the first Ukrainian cities to come under attack from Russian forces when the invasion began three weeks ago.

Ukrainian President Volodymyr Zelenskyy called for more help for his country in a video address to German lawmakers, saying thousands of people have been killed so far, including 108 children.

He also referred to the dire situation in Mariupol. “Everything is a target for them,” he said, including “a theater where hundreds of people found shelter that was flattened yesterday.”

The address began with a delay because of a technical problem caused by “an attack in the immediate vicinity” of where Zelenskyy was speaking from, Bundestag deputy speaker Katrin Goering-Eckardt said.

Zelenskyy's address to the Bundestag came a day after he delivered a speech via video to the U.S. Congress that garnered several ovations as he called for more help.

Zelenskyy's office said Russia carried out further airstrikes on Mariupol early Thursday, as well as artillery and airstrikes around the country overnight, including in the Kalynivka and Brovary suburbs of the capital, Kyiv. There was no immediate word on casualties.

In Kyiv, where residents have been huddling in homes and shelters, emergency services said a fire broke out in an apartment building hit by remnants of a downed Russian rocket early Thursday, killing one person and injuring at least three.

Firefighters evacuated 30 people from the top floors of the 16-story building and extinguished the blaze within an hour.

Russian artillery destroyed a school and a community center in Merefa, a city near the northeast city of Kharkiv, according to Merefa's mayor Veniamin Sitov. There were no known civilian casualties. The Kharkiv region has seen heavy bombardment as stalled Russian forces try to advance in the area.

The UN Security Council is to meet on Thursday at the request of six Western nations that sought an open session on Ukraine ahead of an expected vote on a Russian humanitarian resolution that they have sharply criticized for making no mention of Moscow's war against its smaller neighbour.

“Russia is committing war crimes and targeting civilians,” Britain's UN Mission tweeted, announcing the call for the meeting that was joined by the US, France and others. “Russia's illegal war on Ukraine is a threat to us all.”

Russian President Vladimir Putin went on television Wednesday to excoriate

Russians who don't back him.

Russians “will always be able to distinguish true patriots from scum and traitors and will simply spit them out like a gnat that accidentally flew into their mouths,” he said.

“I am convinced that such a natural and necessary self-purification of society will only strengthen our country.”

He said the West is using a “fifth column” of traitorous Russians to create civil unrest.

“And there is only one goal, I have already spoken about it — the destruction of Russia,” he said.

The speech appeared to be a warning that his authoritarian rule, which had already grown tighter since the invasion began on February 24, shutting down Russian news outlets and arresting protesters, could grow even more repressive.

In a sign of that, Russian law enforcement announced the first known criminal cases under a new law that allows for 15-year prison terms for posting what is deemed to be “false information” about the Ukraine war.

Among those charged was Veronika Belotserkovskaya, a Russian-language cookbook author and blogger living abroad.

Both Ukraine and Russia this week have reported some progress in negotiations. Kremlin spokesman Dmitry Peskov said talks should continue on Thursday in some form.

Some negotiators were breaking into working groups, “but there should be contacts today,” he said during his daily conference call with reporters.

He also said Moscow “can't take into account” an International Court of Justice ruling ordering Russia to halt its operation in Ukraine, noting that both sides need to agree on implementing the ruling, and on Russia's side “there can be no consent.”

Talks held by video Wednesday appeared to wade deeply into technicalities.

Zelenskyy adviser Mikhailo Podolyak said Ukraine demanded a cease-fire, the withdrawal of Russian troops and security guarantees for Ukraine from several countries.

An official in Zelenskyy's office told The Associated Press that the main subject under discussion was whether Russian troops would remain in separatist regions in eastern Ukraine after the war and where the borders would be.

The official, speaking on condition of anonymity to discuss the sensitive talks, said Ukraine was insisting on the inclusion of one or more Western nuclear powers in the negotiations and on a legally binding document with security guarantees for Ukraine. In exchange, the official said, Ukraine was ready to discuss a neutral military status.

Russia has demanded that NATO pledge never to admit Ukraine to the alliance or station forces there.

The fighting has led more than 3 million people to flee Ukraine, the U.N. estimates. The death toll remains unknown, though Ukraine has said thousands of civilians have died.