There are reports the Russian military has begun storming the last pocket of Ukraine resistance at the Azovstal steelworks in Mariupol where hundreds of civilians remain trapped in an underground “hell”.

A number of Ukraine officials, including the Mariupol patrol police chief and a commander of Ukraine’s National Guard, have told media the enemy had “started to storm the plant in several places” using armoured vehicles.

It comes as the first evacuees from the plant reached safety and have been experiencing sunshine on their faces after surviving two months in dark bunkers with little food and water while Russian bombs rained down.

A convoy of civilians, including women and children, who were evacuated from the Azovstal steelworks and wider Mariupol area arrived in the Ukraine-held city of Zaporizhzhia after a 200km bus journey.

Women and children arrive to sunshine in Zaporizhzhia. Photo: AAP

The Red Cross said it was pleased the complex rescue operation from the steel plant, which involved avoiding landmines and an artillery strike, was a success, but hundreds more people remained trapped in “hell”.

“You can imagine the situation they endured for many weeks, and as they told us, it was just terrible,” said Ukraine’s delegation for Red Cross Pascal Hundt.

“The testimonies we have received are just heart-breaking. Nonetheless, we managed to help and facilitate the safe passage of a few.

“But, we would have hoped that…more people would have been able to join the convoy to get out of hell.”

One young mother told the BBC it was impossible to sleep as the Russian military relentlessly attacked the sprawling industrial plant where hundreds had been taking shelter in a system of underground tunnels and bomb shelters.

“From the morning and during the night we were bombarded. Artillery, rockets, air strikes. Our children couldn’t sleep. They were crying. They were scared. And us as well,” said Katarina.

“There were several times when we were losing hope that we would ever get out. We are extremely glad to be in Ukraine.”

Food and shelter at a centre for displaced people in Zaporizhzhia. Photo: AAP

For those who remained underground at the Azovstal factory, the bombardment continued after Russia launched another attack.

In a Telegram video, Captain Sviatoslav Palamar of the Azov Regiment — a Ukrainian ultra-nationalist militia — said Russia pounded the steel works with naval and barrel artillery through the night and dropped heavy bombs from planes.

Reuters could not independently verify his account.

“As of this moment, a powerful assault on the territory of the Azovstal plant is under way with the support of armoured vehicles, tanks, attempts to land on boats and a large number of infantry,” Palamar said.

He added that two civilians were killed and 10 injured, without providing evidence.

Russia’s defence ministry said Ukrainian forces had used the ceasefire at Azovstal to establish new firing positions, and that Russia-backed forces were now “beginning to destroy” those positions.

Meanwhile UK Prime Minister Boris Johnson has become the first world leader to address Ukraine’s parliament since the invasion.

Mr Johnson praised Ukraine’s determined resistance to Russia’s military might, saying it was Ukraine’s “finest hour” that would be remembered and recounted for generations to come”.

“You have exploded the myth of Putin’s invincibility and you have written one of the most glorious chapters in military history and in the life of your country,” he said.

“The so-called irresistible force of Putin’s war machine has broken on the immoveable object of Ukrainian patriotism and love of country.”

A man welcomes Anna and her son Svyatoslav who were evacuated from Mariupol. Photo: AAP

Giving an update on the battle front, Ukraine’s general staff said its forces were defending the approach to Kharkiv from Izyum, a town on the Donets river, some 120km to the southeast, as the enemy left a trail of destruction in Luhansk province.

Some other areas of Donetsk were under constant fire and regional authorities were trying to evacuate civilians from frontline areas, the Ukrainian president’s office said.

Russian shelling killed at least three civilians in the town of Vuhledar, the president’s office said. Ukraine’s military said Russian forces were trying to take the frontline town of Rubizhne.

Reuters could not independently verify Ukraine’s battlefield accounts.

Heavy clashes were taking place around Popasna, in Luhansk. Shelling was so intense it was not possible to collect bodies, said regional Governor Serhiy Gaidai.

-with AAP