Sixty civilians died in the bombing of a school in eastern Ukraine's Lugansk region this weekend, President Volodymyr Zelensky said on Sunday.

"Just yesterday in the village of Bilogorivka, Lugansk region, a Russian bomb killed 60 people. Civilians," Zelensky said during an address to the G7 summit by video conference.

"They were hiding from shelling in the building of a regular school, which was attacked by a Russian airstrike."

Lugansk governor Sergiy Gaiday told Russian-language television station Current Time TV that 60 people died under the rubble after an "aerial bomb" struck the village school on Saturday.

"There are very serious shellings in Bilogorivka. The fighting has been going on since morning," he added.

"I would really like to believe that people are still alive there, and as soon as the shelling ends, we will be able to start clearing the rubble."

Earlier Sunday, Gaiday had said 90 people had been at the site when the strike hit and that 27 had been saved.

Rescuers could not work overnight because of a threat of new strikes but resumed their work Sunday.

They were also looking for survivors in the neighbouring village of Shepilivka after a strike hit a house where 11 people were sheltering in the basement, Gaiday said.