After nearly two months under siege, civilians holed up at a steel plant in the Ukrainian city of Mariupol began to be evacuated over the weekend.
Local officials said people sheltering elsewhere in the besieged city were allowed to leave on Monday.
Video posted online a day earlier by Ukrainian forces showed elderly women and mothers with small children climbing over a steep pile of debris out of the sprawling Azovstal site's rubble and eventually boarding a bus.
Denys Shlega, commander of the 12th Operational Brigade of Ukraine's National Guard, claims that several hundred civilians remain trapped alongside nearly 500 wounded soldiers and "numerous" dead bodies.
"Several dozen small children are still in the bunkers underneath the plant," Mr Shlega said.
As many as 100,000 people may still be in Mariupol, including an estimated 2,000 Ukrainian fighters beneath the sprawling, Soviet-era steel plant – the only part of the city not occupied by the Russians.
More than 100 people were expected to arrive in the Ukrainian-controlled city of Zaporizhzhia on Monday, according to President Volodymyr Zelensky.
"Today, for the first time in all the days of the war, this vitally needed (humanitarian) corridor has started working," Mr Zelensky said on Sunday.
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However, there were safety concerns, as people fleeing Russian-occupied areas have described their vehicles being fired upon, and Ukrainian officials have repeatedly accused Kremlin forces of shelling after agreeing evacuation corridors.
A Ukrainian defender of the steel plant urged groups such as the UN and the Red Cross to ensure the safety of those being evacuated.
Sviatoslav Palamar, deputy commander of the Azov Regiment, told the Associated Press in an interview that there should be guarantees from "a third party – politicians, world leaders – who will cooperate to negotiate with Russians to extract us from here".
Another of the plant's defenders said Russian forces resumed shelling on Sunday as soon as the evacuation of a group of civilians was complete.
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Mariupol, a port city on the Sea of Azov, has seen some of the worst suffering.
A maternity hospital was hit in a Russian air strike at the start of the conflict, and hundreds of people were reported killed in the bombing of a theatre.
The city is a key target because of its strategic location near the Crimean Peninsula, which Russia seized from Ukraine in 2014.
Mr Palamar, said it has been difficult even to reach some of the wounded in the steel plant.
"There's rubble. We have no special equipment," he said.
"It is hard for soldiers to pick up slabs weighing tons only with their arms.
"We hear voices of people who are still alive (inside shattered buildings)."