Serhiy Hayday, head of the Luhansk regional military administration, said the school building was destroyed.
"The explosion happened inside the building. Rescuers (are) dismantling the debris as quickly as possible. The chances of finding (anyone still) alive are very small. There were 90 people inside the school building; 27 survived, 60 people most likely died," Hayday said.
Hayday said a Russian air strike hit the school in the village of Bilohorivka, which is some seven miles from the front lines of the ongoing conflict in eastern Ukraine, at around 4:37 p.m. (9:37 a.m. ET) on Saturday, causing fires to break out that took almost four hours to extinguish.
Photos shared from the scene showed rescue personnel searching the smoldering ruins of the school building.
Survivors of the bombing described their harrowing experience in interviews with CNN.
"I got slammed down by a slab -- bent into a ball," said a man with a bandage across his nose and forehead, who preferred not to give his name out of privacy concerns. "Then another explosion, small rocks fell on us. Darkness."
He continued: "There was a woman in our room screaming the whole time. She was pulled out and screaming the whole time. I told her, 'Don't scream.' We couldn't hear a thing."
"They started digging," he said. "I got out. I was like a drunk man -- lost."
Video of the school shared by Hayday on Telegram shows a building that was completely leveled by the attack.
Another survivor, Sergiy, said that he was in the school's basement when the bomb hit and that all three floors of the building collapsed "to the ground."
"We didn't understand anything," Sergiy said. "We were inside. All at once, everything fell down. Darkness. That's it."
Yevgen, meanwhile, described a desperate escape.
"I was the very first one to start climbing out," he said. "I was raking bricks and throwing them out. There were wooden planks and boards. Locals who weren't in the basement helped and used a pipe to rip those boards off."
The survivors said that among the neighbors they were sheltering with were several elderly grandparents.
"Imagine what they bombed," said Sergiy. "An ordinary village with only pensioners and children."
United Nations Crisis Coordinator for Ukraine and UN Assistant Secretary-General Amin Awad in a statement Sunday called the bombing "yet another stark reminder of the cruelty