A third evacuation from the war-ravaged Ukrainian city of Mariupol is underway, UN-Secretary General Antonio Guterres announced on Thursday.

Guterres told the Security Council that two prior safe passage agreements resulted in "a measure of success" with 480 civilians being able to escape the strategic port city that has been largely leveled by Russian bombardment.

The third evacuation began on Thursday morning, and Guterres refrained from speaking about any of its details before it is completed in order "to avoid undermining possible success."

"I hope that the continued coordination with Moscow and Kyiv will lead to more humanitarian pauses to allow civilians safe passage from the fighting and aid to reach those in critical need," said Guterres. "We must continue to do all we can to get people out of these hellscapes."

Civilians in Mariupol have had to endure dire humanitarian conditions, including critical shortages of power, food and water amid Russia's ongoing military offensive to capture what remains of the key city.

Thousands of besieged Ukrainian fighters are cornered in an underground tunnel network at Mariupol's Azovstal steel plant alongside the hundreds of civilians estimated to remain there.

Martin Griffiths, who has led Guterres' efforts to broker a nationwide ceasefire, said "elements of diplomatic progress are coming in to view even as the human suffering mounts."

That includes over 13 million Ukrainians who have been forced to flee their homes, including roughly 7.7 million who have been displaced internally, Griffiths said.

"Lives have been uprooted, ripped apart and never will be the same again, and many others couldn't run," he said. "The elderly, people with disabilities, have been unable to seek shelter from bombs, get out to gather supplies, or receive information on evacuations and the threat of."/aa