Twenty civilians were evacuated from a besieged plant in Mariupol, Ukraine.

Conditions in a massive network of tunnels beneath Mariupol's Azovstal steel mill, where hundreds of civilians and Ukrainian fighters are reported to still be hiding, are claimed to be harsh, and previous attempts at evacuations were unsuccessful.

On Saturday, at least 20 civilians, including many children, were able to escape a critically damaged steel plant in Mariupol, Ukraine's port city, in what could be the start of a long-awaited, bigger evacuation of the city's final holdout.

The 20 civilians had departed, according to Ukrainian forces from the Azov regiment, who have been guarding the site. They may have gone to the Ukrainian city of Zaporizhzhia, about 225 kilometres (140 miles) to the northwest.

The Tass news agency in Russia reported a similar story, albeit it estimated the number of evacuees as 25.

A UN-led evacuation had been planned, though it was unclear whether Saturday's evacuation was conducted by the UN and whether more evacuations were on the way. There were no immediate information available on the situation.

Sweden's defence officials announced Saturday that a Russian reconnaissance plane had briefly breached the northern country's airspace the day before, as the country considers a NATO membership bid.