Before the war, Mariupol had a population of about 400,000, but this has fallen to around 100,000 in recent weeks, with those remaining facing a daily struggle with severe shortages of food, clean water, and electricity.
Ukraine's president Volodymyr Zelenskyy has described the situation in Mariupol as "hell", while Ukrainian fighters prepare for what could be their final stand against Russia.
It is estimated that around 2,000 Ukrainian fighters are in tunnels underneath the Azovstal steel plant. They are the last pocket of resistance in a city almost destroyed by two months of intense bombardment.
It is also believed there are still a few hundred civilians trapped in the plant, although Mr. Zelenskyy said that more than 150 people from the steel plant and more than 300 people from the city's suburbs had been evacuated this week.
Speaking in the early hours of Friday, Mr. Zelenskyy said: "Currently, Russian shelling and assault of Azovstal do not stop, but civilians still need to be taken out - women, children, many children who are still there.
"Just imagine this hell.
"And there are children.
"More than two months of constant shelling, bombing, constant death nearby."
He praised the city's Ukrainian defenders, saying that many of them are wounded "but they do not give up - they are holding positions".
Key developments:
• An American official has said that the US shared intelligence with Ukraine about the location of the Russian flagship Moskva before the mid-April strike that sank it, although the decision to target the missile cruiser was Ukraine's• Belarus president Alexander Lukashenko, whose country was used by Russia as a launchpad for the invasion, said Russia had been right to invade Ukraine but he had not expected the conflict to "drag on this way"• Ukraine said at least five people were killed and dozens injured in shelling of cities in the Donbas region over the past 24 hours. Shells hit schools, residential buildings, and a medical facility• Mr. Zelenskyy has launched United24, a platform to raise funds for mine-clearing and post-war reconstruction, while Poland hosted a conference of international donors that raised £5.2bn for humanitarian aid• The mayor of the western Ukrainian city of Ivano-Frankivsk told residents to head for the countryside over the long weekend, due to fears of new attacks• Mr. Zelenskyy praised Britain for its support, saying: "If everyone in the world - or at least the vast majority - were steadfast and courageous leaders as Ukraine, like Britain, I am sure we would have already ended this war and restored peace throughout our liberated territory for all our people". It came after Prime Minister Boris Johnson addressed Ukraine's parliament earlier this week.