Zelensky says around 100 civilians are being evacuated from the Mariupol steel factory.

An evacuation of civilians from Mariupol was underway on Sunday as women and children confined to bunkers beneath a sprawling steel plant started to make their way to safety, according to Ukrainian officials and the United Nations.

President Volodymyr Zelensky said that about 100 civilians were being evacuated from the Azovstal factory and are heading to a “controlled area.”

“Tomorrow we’ll meet them in Zaporizhzhia,” he wrote on Twitter. He said that they were working with the United Nations and other international groups to evacuate more people.

The International Committee of the Red Cross confirmed that it was assisting in a “safe passage operation” in coordination with the United Nations as well as Ukrainian and Russian authorities.

While a handful of people were evacuated on Saturday — with estimates by the Ukrainians and Russians ranging from 20 to 46 — the I.C.R.C. said that “no details can be shared until the situation allows, as it could seriously jeopardize the safety of the civilians and the convoy.”

A U.N. official confirmed that the operation was underway but said details would be available only when it was clear that people had made it to safety.

It was not clear if the evacuation would include just people trapped in the steel plant, where several hundred civilians have sought refuge with hundreds of Ukrainian soldiers, or if people would also be taken from the city itself. Before the war, some 450,000 people lived in the port city. There are now estimated to be around 100,000 people living in the ruins of the destroyed metropolis.

Ukrainian officials have said more than 20,000 civilians have been killed and have accused the Russians of digging mass graves to hide the extent of the slaughter.

The Mariupol City Council confirmed that an evacuation effort was underway, writing on Telegram that people should gather at 4 p.m. near what has formerly been a shopping center known as “Port City.”

“If you have relatives or acquaintances in Mariupol, try to contact them in all ways,” the City Council wrote. “Call, write and say that it is possible to go to Zaporizhzhia, where it is safe.”

The I.C.R.C. said that a convoy of vehicles began making its way to Mariupol on April 29 and traveled 150 miles before arriving on Saturday morning.