Terrifying video from a mass shooting in Russia is going viral online ... and, it paints a dramatic picture of the devastating attack that's left dozens dead and many more injured.
Footage from the chaotic scene Friday at Crocus City Hall -- a huge concert venue on the outskirts of Moscow -- captures the sound of gunshots echoing throughout the cavernous venue.
Another clip shows people hitting the floor, huddling behind chairs in the hall as the sound of gunshots reverberates around the room.
Even worse, a huge fire was ignited at the building -- easy to see from all around the venue -- and the flames themselves seemed to burn strong for a while based on video shot from outside the building. Reports say grenades and or bombs were set off in this bloodbath.
Russia’s Federal Security Service -- the country's organization in charge of domestic security -- says more than 40 people were killed in the attack and more than 100 were injured.
The Associated Press -- citing Russian news outlets -- reports several gunmen entered the building and threw explosives, causing the fire to break out. Men in fatigues reportedly entered the hall and began firing on the crowd in attendance to see Picnic, a popular rock band. Russia's foreign ministry is calling this a terroristic attack.
Some videos reportedly show as many as four gunmen shooting people at point-blank range ... and it appears police detained at least one potential suspect -- seen on video patting down a man with his hands on the side of a vehicle.
BTW ... it seems the U.S. and other major Western powers might've seen this coming -- with warnings to their citizens being issued in recent weeks to stay away from crowded areas in Moscow.
It's not yet clear if this attack was sparked by any political motives ... but, state authorities are investigating it as an act of terror.