Local news channel 78 News quoted unnamed sources as saying that at least 3 people were killed and many others were injured in the explosion that occurred on February 17 in the town of Sertolovo, north of Russia's second largest city.
Local news site 47 News, citing emergency forces sources, also confirmed 3 deaths from this large explosion.
Images shared by many media outlets show that the 2 upper floors of the building collapsed, surrounded by large piles of rubble.
Leningrad Governor Alexander Drozdenko said that the cause of the explosion that collapsed part of the building is being investigated.
Russian troops and security forces have been dispatched to the scene to clear the rubble and search for possible trapped victims.
Russian news site Lenta. ru reported that there is still concern that the building may continue to collapse further.
The Russian Investigative Committee, the agency in charge of investigating serious crimes, announced that it has opened an investigation into the possibility of violations of fire safety regulations.
Initially, it was determined that there were casualties caused by the incident" - this agency added.
The large explosion occurred right at the time the round of negotiations between Russia and Ukraine mediated by the US began in Geneva, Switzerland.
Observers assess expectations for the 2 days of negotiations as low, as both sides seem unwilling to compromise on key issues related to territory and future security.
Since the Russia-Ukraine conflict broke out nearly 4 years ago, Russia has regularly recorded sabotage incidents targeting military bases and civilian infrastructure.
Gas leaks are a common cause of explosions at construction sites from the Soviet era in Russia, although officials have not yet given any signs that this is the cause of this incident.
