Several gunmen burst into a big concert hall in Moscow on Friday and fired automatic weapons at the crowd, killing at least 40 people, injuring more than one hundred others and starting a massive blaze, in an apparent terror attack days after President Vladimir Putin cemented his grip on the country in a highly orchestrated electoral landslide.

Russian news reports said that the assailants threw explosives, triggering a massive blaze at the Crocus City Hall on the western edge of Moscow. Video posted on social media showed huge plumes of black smoke rising over the building.

The attack took place as crowds gathered for a concert of Picnic, a famed Russian rock band, at the hall that can accommodate over 6,000 people. Russian news reports said that visitors were being evacuated, but some said that an unspecified number of people could have been trapped by the blaze.

Russia’s state RIA Novosti news agency reported that at least three people in combat fatigues fired weapons. The state Tass news agency also reported the shooting.

Extended rounds of gunfire could be heard on multiple videos posted by Russian media and Telegram channels. One showed two men with rifles moving through the mall. Another one showed a man inside the auditorium, saying the assailants set it on fire, as gunshots rang out incessantly in the background.

More videos showed up to four attackers, armed with assault rifles and wearing caps, who were shooting screaming people at point-blank range. (AP)