The search continues for the son of two prominent New Zealand doctors reported missing while working in Ukraine.

Andrew Bagshaw, son of well-known Christchurch doctors Philip and Sue Bagshaw, was reported missing on Monday.

He had been volunteering to assist the people of Ukraine by delivering humanitarian aid.

Grzegorz Rybak was with Bagshaw, helping evacuate people and animals from the Ukrainian city of Bakhmut.

He speaks English, Polish and Russian, and translated for Bagshaw as they worked to provide relief for the region.

He says the humanitarian situation there is harrowing.

"We were delivering food, sanitary pads, encouraging people to evacuate."

Rybak says there has been those reluctant to leave their homes and belongings behind.

Andrew's parents say he volunteered in Ukraine because it was the morally right thing to do.

Rybak says he's hugely respected for his work there.

He has been sharing a flat with Bagshaw for two weeks. He says the people still searching for him are exhausted, both physically and emotionally, but they're keeping up the search as best they can.

"The police are looking for him, the army is looking for him, he's gained huge respect."

Rybak says Andrew showed humanity at the highest level through the work he's doing in Bakhmut.

While Rybak does not know what happened to Bagshaw, he believes if he is alive and likely in Russian hands.

The difficulty in tracking him down, says Rybak, is the lack of cell phone reception or electricity throughout the region.

He hopes his friend is in hiding.

"I hope that he will be found in a cellar somewhere. I don't say it's optimistic but, of course, hope does last."

Philip and Sue Bagshaw say agencies from New Zealand and the UK, where their son was born, are working hard to find him.

Former Defence Minister Wayne Mapp says it's likely the efforts to find Bagshaw are being co-ordinated by the UK.

The British government, which has far more diplomatic representation in the area, will be doing as much as they can, working with Ukrainians and the aid organisations to locate Bagshaw, he says.

So far, the New Zealand government has taken an appropriate level of effort in responding to the war in Ukraine, Mapp says.

New Zealand has supplied trainers and intelligence officers to support the Ukrainian army, as well as humanitarian aid.

Andrew's parents say their son is an intelligent, independently minded person who they love dearly, and they were grateful to everyone who was searching for him.

A British aid worker, Christopher Parry, is also missing in Ukraine and disappeared at the same time as Andrew Bagshaw.

-Finn Blackwell/RNZ.