The attack was one of Russia's deadliest against Ukraine this year, the Reuters news agency reported.
At least 50 people were wounded, it reported, with the emergency services saying that the figure was growing.
More than 30 people, including a three-month-old baby, were in hospital, regional governor Serhiy Lysak said, as cited by Reuters.
President Volodymyr Zelensky said in a video message that rescue efforts were underway in the city, his hometown. He called on the West to exert greater pressure on Moscow.
"All Russian promises end with missiles, drones, bombs or artillery. Diplomacy means nothing to them," he said.
"That is why Russia must be put under sufficient pressure so they feel the consequences of every lie, every strike, every day they take lives and prolong the war," he added.
Russia launched a full-scale invasion of Ukraine on February 24, 2022, starting the largest armed conflict in Europe since World War II.
Friday is day 1,135 of Russia's war on Ukraine.
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Source: Reuters, IAR, PAP, Ukrinform, president.gov.ua