The blast, in the city's Prospekt Mira region, shattered glass, crushed stairwells, and ripped off the facade of the seven-story building, leaving at least 10 apartments exposed.
Two women were reported killed. Among the injured was a child, who is reported to be in a critical condition. Rescue workers say the number of fatalities is likely to grow as more people are uncovered from the wreckage.
The cause of the explosion is believed to be an accidental gas leak. Russian news agencies report that one of the apartments in the building was undergoing illegal reconstruction work. Residents of the building said members of the construction team were seen drinking heavily on 6 December.