St Petersburg Governor Alexander Beglov said "an incident" had taken place in the city's north-eastern district of Krasnogvardeyskiy. There were no casualties, but residents were evacuated from their apartments, Beglov said, without explaining the cause of the incident or its nature.

Reuters video taken at the scene showed a damaged facade of a building with blown-out windows, damaged balconies and shattered glass and debris on the ground.

Citizens of the damaged houses told Reuters that they heard some strange sounds followed by a blast and a fire.

"I first heard a whistle, because I had just opened the window, then a pop, a blaze and a full apartment of smoke, the window flew out," local resident Elena told Reuters. She said this happened after 0700 local time (0400 GMT).

Russian media outlets reported that the incident could have been caused by a downed Ukrainian drone, which was heading towards a nearby fuel depot. There was no official confirmation of this from Russia authorities or state media.

(Reporting by Reuters; writing by Maxim Rodionov; editing by Jason Neely)