The blast in Volgograd, 900km southeast of Moscow, occurred about midday in an apartment on the seventh floor of the nine-story structure. Much of the building’s exterior wall on one side was blown off and fire spread to other floors.

Oleg Grebenyuk, head of the emergency ministry’s Volgograd division, was quoted by the Tass news agency as saying one body had been found and that rescuers thought about a dozen people could be under the debris. He didn’t clarify if there were signs that anyone might be alive but trapped.

About 150 people lived in the section of the building affected by the blast, said Vladimir Markin of the Investigative Committee. Those forced to leave were being housed in a local school.