Russian hotel owner Mikhail Golubtsov says it was partly the shame he feels over Russia's invasion of Ukraine that persuaded him and his family to take in Ukrainians fleeing the fighting - 34 so far, and counting.

The Russian former construction engineer left his home country in 2014 over Moscow's "unacceptable" annexation of Crimea, and now runs a modest but cosy hotel in the green hills of central Serbia.

Prior to Moscow's launch of what it terms a "special military operation" in Ukraine on Feb.24, Golubtsov's guests were mostly city folk on weekend trips to the countryside. Now most rooms are taken up by Ukrainian refugees, who can stay at the hotel free of charge, for as long as they need.

"The first seven people arrived because a friend gave them the address, ... now they are simply arriving," said Golubtsov, 58, as he brought boiled fruit and chocolates to a group of children playing with dogs in the sunshine.

"At first (after the invasion started), I was in shock and I was so ashamed. For some time I could not speak Russian, but when guests arrive and they speak Russian to me, I speak Russian as well. I think the only thing I can do now is to help Ukrainians somehow," he said.

The United Nations says 3.8 million Ukrainians have fled abroad since the war began, most of them to Poland and Romania. Only around 2,500 have come to Serbia so far, mostly as a stopover on their journey to western Europe.

One of his guests was Anna Nizhegorodova, 46, a Russian married to a Ukrainian who had been living in Kyiv for the past 15 years. Her two children aged nine and 16 were also with her.

Nizhegorodova said that after several days in Kyiv bomb shelters she and her Ukrainian friend Olga Manmar, an English teacher and mother of three, decided to leave, packing everything in two cars and joining refugee columns heading to Romania.

After several days, the group ended up in Golubtsov's hotel near the town of Batocina, about 100 km (60 miles) southwest of Belgrade.

Nizhegorodova said she "felt nothing" when she arrived.

"In your mind you understand that everything around you is very beautiful and very quiet, but ... you simply want to cover yourself with a blanket," she said.

Manmar, 39, broke into tears when describing how Ukrainian families were forced to part at the Romanian border. Ukraine has banned able bodied men from leaving the country.

"(When) you cross the border, ... you are safe, ... but you feel sorry for those who could not," she said speaking in English.