ST PETERSBURG (Reuters) -A drone crashed into a five-storey residential building in St Petersburg on Saturday and 100 people were evacuated with no casualties, Russia's Rosgvardiya national guard said.

       St Petersburg Governor Alexander Beglov said earlier that two buildings were damaged and residents had been evacuated after what he called an "incident" with no casualties.

       Beglov did not explain the cause or nature of the incident, but local residents told Reuters that they had heard a strange sound followed by a blast and a fire on Saturday morning.

       "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).

       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.

       Russian media outlets reported that the incident could have been caused by a downed Ukrainian drone, which was heading towards a nearby fuel depot.

       Ukraine's defence ministry said it "did not possess information about the indicated situation".

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       (Reporting by Reuters; writing by Maxim RodionovEditing by Jason Neely and Mark Potter)