The accident, which occurred at about 9:00 a.m. (6:00 a.m. GMT) between Valdai and St. Petersburg, set ablaze three buildings located some 100 meters (320 feet) from the pipeline. Two of the buildings burned down to the ground.
No casualties were reported, however, and the fire was extinguished at around 10:30 a.m. (7:30 a.m. GMT.)
Gas supplies via the pipeline have been halted, and supplies to the region are being pumped through alternative channels.
"The fire has been put out, the repairs are underway and we plan to finish them in around 24 hours," the spokesman said.
"The accident resulted in a six-meter or so (20-foot) hole in the pipeline. Parts of the pipe were thrown some 50 metres (160 feet) from the pipeline" he added.
Traffic was delayed for two hours on the busy Moscow-St. Petersburg highway.
Russian Emergency Ministry experts said the accident could have been caused by metal fatigue.