Several gunmen opened fire at a popular concert venue on the Moscow outskirts on Friday, Russia’s state news agencies reported.

The Russian news agency TASS said eyewitnesses had reported “killed and wounded” at the venue, Crocus City Hall, without specifying a number. Reports on social media said dozens had been wounded and up to 12 were dead, but those figures were not immediately confirmed by the Russian authorities.

“At least three people in camouflage burst into the ground floor of Crocus City Hall and opened fire with automatic weapons,” a correspondent for another news agency, RIA Novosti, reported from the scene. “There are definitely wounded.”

Moscow’s mayor, Sergei S. Sobyanin, said that a “terrible tragedy” had occurred.

Videos verified by The New York Times show multiple people holding guns and entering Crocus City Hall, a shopping mall and concert venue in Krasnogorsk, a suburb on the northwestern outskirts of Moscow. The videos show people wounded on the ground.

In videos filmed inside the concert hall, audience members awaiting an upcoming performance by the veteran rock band Piknik are heard screaming and repeated gunshots are heard from outside the hall. Other videos filmed from a highway outside of the building show parts of it on fire, producing heavy smoke.

According to RIA Novosti, the Moscow regional governor arrived on the scene shortly after emergency-services personnel.

On March 7, the U.S. Embassy in Moscow issued a security alert warning that its personnel were “monitoring reports that extremists have imminent plans to target large gatherings in Moscow, to include concerts.” The statement warned U.S. citizens that an attack could take place in the next 48 hours.