Local sources wrote of the deafening blast on Twitter, asking whether the flames were caused by a regular fire or another type of explosion.
A clip of the blaze showed flames flowing into a mushroom cloud in the air above what appears to be a forest area in Vsevolozhsk, a residential area around 24km (15 miles) east of St Petersburg.
State media has claimed that the explosion was caused by an erupting gas pipeline that runs through the Leningrad region.
The local governor said there is no threat to locals and that the fire is under control.
It comes just hours after an explosion caused by a gas leak in a residential building killed at least nine people, including four kids, on the Russian island of Sakhalin.
The blast happened on the Russian territory island of Sakhalin, which is in the Pacific Ocean, just north of Japan.
A gas cylinder erupted in one of the apartments at around 5.30am local time this morning.
Ambulance crews are reportedly working in the courtyard of the house and surgeons are operating on the victims close to the scene, according to local site tvzvezda.
Emergency responders are searching through the rubble in case there are more bodies trapped. More than 50 people, including volunteers, are involved in the operation.
Thirty-three people were known to have lived in the building but three are still unaccounted for, reports say.
Drones and helicopters were used to help find the victims, according to tvzvezda.