The attack, which also saw a massive blaze, comes days after President Vladimir Putin cemented his grip on the country in a highly orchestrated electoral landslide.
There were no immediate claims of responsibility for the raid, the worst terror attack in Russia in two decades that came as the fighting in Ukraine dragged into a third year.
According to Russian news reports, the assailants hurled explosives, igniting a massive blaze at the Crocus City Hall situated on the western outskirts of Moscow.
Social media footage depicted extensive plumes of black smoke billowing over the building.
The assault occurred during a Picnic concert, a renowned Russian rock band, as crowds gathered in the venue, which has a capacity of over 6,000 people.
According to Russian news reports, visitors were being evacuated from the scene, although there are concerns that an unspecified number of individuals may have been trapped by the raging blaze.
The prosecutor’s office confirmed that several individuals dressed in combat fatigues entered the concert hall and opened fire on attendees.
Numerous videos shared by Russian media and Telegram channels captured extended rounds of gunfire echoing inside the venue.
One video depicted two individuals armed with rifles moving through the mall, presumably in search of targets.
In another footage, a man inside the auditorium described the assailants setting the area ablaze, amidst a continuous barrage of gunfire echoing in the background.
Additional videos surfaced showing up to four attackers armed with assault rifles and wearing caps, ruthlessly shooting at screaming individuals at point-blank range.
Andrei Vorobyov, the governor of the Moscow region, announced that he was en route to the area and had established a task force to address the situation’s aftermath.
However, he did not provide immediate additional details regarding the ongoing incident.
Russian media reports indicate that riot police units are being dispatched to the area as evacuations continue.
Authorities have announced heightened security measures at Moscow’s airports and railway stations.
Additionally, the Moscow mayor has canceled all mass gatherings scheduled for the weekend in response to the unfolding situation.
White House national security adviser John Kirby expressed his inability to discuss all the details at the moment, but he acknowledged the distressing nature of the images emerging from the incident, describing them as “just horrible” and “hard to watch.”
“Our thoughts are going to be with the victims of this terrible, terrible shooting attack,” Mr Kirby stated.
“There are some moms and dads and brothers and sisters and sons and daughters who haven’t gotten the news yet. This is going to be a tough day.”
The attack occurred following a statement issued earlier this month by the US embassy in Moscow, urging Americans to avoid crowded places in the Russian capital due to the possibility of an imminent attack.
This warning was echoed by several other Western embassies, highlighting the heightened concerns regarding security in the region.
Mr. Putin, who solidified his control over Russia for another six years in the March 15-17 presidential vote following a significant crackdown on dissent, recently denounced the Western warnings as an effort to intimidate Russians.
This response underscores the ongoing tensions between Russia and Western nations.
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