Mourners gathered at a Kyiv church on Sunday to honour Andrew Bagshaw, one of two British volunteers who died as they were evacuating civilians from fierce fighting in Ukraine's Donetsk region.

Bagshaw, 47, and Chris Parry, 28, were reported missing in early January after having set out for the town of Soledar, which saw heavy fighting in recent weeks between Ukrainian and Russian forces.

Their families confirmed their deaths this week, with a statement from Bagshaw's relatives saying the pair "were attempting to rescue an elderly woman from Soledar... when their car was hit by an artillery shell".

Concern had grown about their fates after the head of the Russian mercenary group Wagner, which helped capture Soledar from Ukrainian forces, said on January 11 that one of the missing men's bodies had been found there.

Little more was known about what happened, the Bagshaw family said in a statement.

Fellow volunteers who have been risking heavy fighting to evacuate civilians organised a memorial for Bagshaw at a church in the Saint Sophia Cathedral complex in the capital.

They read words from Bagshaw's family, including his parents, who wrote they were "devastated that he's gone".

"We take comfort in that he found fulfilment and meaning in his work in Ukraine."

Bagshaw's remains will be returned to New Zealand where he and his family lived.

- 'Completely immersed' -
 

A memorial for Parry would be organised by "those closest to him", volunteer Ignatius Ivlev-Yorke wrote in an Instagram post.

Flowers were laid at the altar after a service, where Archpriest Petro Landvytovych paid tribute to Bagshaw and others "who gathered from all over the world to help the Ukrainian people".

Mykola, 24, met Bagshaw while evacuating people from Soledar and said the older man was "completely immersed" in the work of helping people and had been doing so in Donetsk since March, despite not speaking the language.

"He reacted absolutely unemotionally to everything, he had nerves of steel," he said, despite the pervasive danger.

"Volunteers on the front line are dying. It's all about chance out there, if you are lucky -- you survive."

For Victoria Ivleva, Ivlev-Yorke's mother, concern for her children and other volunteers on the frontlines comes with a mix of feelings.

"Worry of course, pride of course, love of course, anxiety of course, hatred to those who did it and love for those whom they are saving," she told reporters after the ceremony.