Large flames and thick plumes of acrid smoke were seen rising into the air over St Petersburg today.
Local sources wrote of the deafening blast on Twitter, asking whether the flames were caused by a regular fire or another type of explosion.
One wrote: "Is it a fire in St. Petersburg or what? I have never seen or heard such a sound. HUGE flame [...]"
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,
It comes after it emerged that Moscow's commanders have secretly moved almost 100 air defence missiles from Belarus to Russia sparking fears of a bigger escalation in Ukraine including whether Vladimir Putin would use a dirty nuke bomb.
Air-freighting scores of S-300 and S-400s is either a precaution against a retaliation from Ukraine for Russia’s recent blitz - or a sign of a much bigger atrocity yet to come.
One Russia expert told the Mirror: “Whatever Russia has in mind to inflict on Ukraine the Kremlin appears to be expecting retaliation on its own soil from Ukraine or the West.
“Analysts believe with these missile moves done so rapidly, just prior to this week’s massive bombardments, the two are interconnected.
“But more ominously they may indicate that worse may yet be to come and they are preparing for a big reaction to this activity.
“But more ominously they may indicate that worse may yet be to come and they are preparing for a big reaction to this activity.
“There has been talk of a dirty bomb.”
