The first group of evacuees from the besieged Ukrainian town of Mariupol are describing the horrors of what they witnessed as they hid in bunkers beneath a steel plant, all while Russian bombs fell above them.

"When the bunker started to shake, I was hysterical, my husband can vouch for that: I was so worried the bunker would cave in," 37-year-old Natalia Usmanova told Reuters.

Usmanova was among the first group of people to evacuate the ruins of the Mariupol steel plant over the weekend. They had for weeks been living in a system of bunkers beneath the plant, which had been hit with heavy shelling by invading forces since early March.

Some from the group (namely women, children and the elderly) were evacuated to the city of Zaporizhzhia by the United Nations and International Committee of the Red Cross, via an operation coordinated by Ukraine and Russia, Reuters reports.

Another evacuee, 44-year-old Yelena Aytulova, told the outlet how she had been living in a bunker with more than 40 others since the invasion began on Feb. 24.

"For a month we were eating — over 40 of us — six tins of food. We boiled two buckets of soup out of them and that was it for the whole day," she said.

Aytulova described how a group of soldiers escorted 11 people out of the group, including "those who were seriously ill, had asthma or needed insulin and also three of us, randomly."

"More than 40 people, including little children are left there," she added.

Another woman who had been sheltering in a Mariupol bunker told the BBC she had not seen sunlight in two months before being evacuated.

An aide to Mariupol's mayor told Reuters that, once the first convoy of evacuation buses left the factory on Sunday, Russia resumed its shelling of the area.