Russia's second city St. Petersburg was hit by a massive power cut on August 20.
Russian media reports said affected areas included the city center as well as metro stations.
Trolleybuses halted in the middle of the road as the electricity went out. Water supplies were also cut off during the power failure.
The city's international airport, Pulkovo, was reportedly working normally.
Emergency Situations Ministry spokeswoman Irina Andrianova said initial information suggested that the power cut had been caused by a breakdown at a power sub-station, triggering a similar problem at another.
According to the BBC, the lights went back on after about an hour.
compiled from agency reports