With the southern Ukrainian city under steady attack, officials had been waiting for a chance to allow individual burials to resume.

But with morgues overflowing and many corpses uncollected at home, they decided they had to take action.

A deep trench some 25 metres long has been dug in a cemetery in the heart of the city.

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Workers brought 30 bodies wrapped in carpets or bags on Wednesday, and 40 were brought on Tuesday.

Other city workers are also bringing bodies so the numbers being buried are quickly rising and the total in the long grave is now unclear.

The dead include civilian victims of shelling on the city as well as some soldiers.

Workers with the municipal social services have also been collecting bodies from homes, including some civilians who died of disease or natural causes.

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No mourners or families were there - just the workers who made the sign of the cross after pushing the bodies into the common grave.

The city plans to close the grave on Thursday if the bombardments stop long enough to allow workers to do so.

At the gates of the cemetery, a woman was told her mother was among those buried in the trench.

She said she left her body three days before, outside a morgue with a paper label attached stating her name.

Ukrainian officials said three people, including a child, died and at least 17 people were wounded in a Russian airstrike on a maternity and children's hospital on Wednesday, while more than 1,200 civilians in Mariupol are thought to have been killed.

Meanwhile, the West has warned the number of Ukrainian refugees arriving in neighbouring countries could surpass four million within days.

One official described the situation on the borders as "unprecedented".

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So far, the United Nations believes at least 2.3 million people have fled their homes since the conflict began, mostly entering Poland.

Others have travelled to Hungary, Romania, Slovakia and Moldova.