At least 40 people were killed and more than 100 were injured after armed attackers stormed a popular concert venue complex near Moscow and opened fire, according to preliminary information from the Federal Security Service in Russia, state media TASS reported.

Video footage from the site of the attack, the Crocus City Hall concert venue, shows the vast complex on fire with smoke billowing into the air. RIA Novosti reported the armed individuals “opened fire with automatic weapons” and “threw a grenade or an incendiary bomb, which started a fire.”

State media Russia 24 reported the roof on the venue has partially collapsed.

The attack unfolded before the music group Picnic was set to preform, according to Russia 24.

The Russia Prosecutor General’s Office said “Unidentified people in camouflage broke into Crocus City Hall and started shooting before the start of the concert,” according to Russian state media TASS.Video footage showed panic as the attack unfolded, with crowds of people huddling together, screaming and ducking behind cushioned seats as gunshots started echoing in the vast hall.

Regional governor Andrey Vorobyov said everything was being done to save people. A SWAT team was called to the area and more than 70 ambulance teams and doctors were assisting victims.

Around 100 people were evacuated from the building by firefighters, TASS reported. Rescuers are still working to get people off the roof, according to the Main Directorate of the Ministry of Emergency Situations of the Russian Federation.Moscow Mayor Sergei Sobyanin called the attack a “terrible tragedy.”

“Today a terrible tragedy occurred in the Crocus City center. My condolences to the loved ones of the victims. I gave orders to provide all necessary assistance to everyone who suffered during the incident,” Sobyanin said in a statement.

Sobyanin said on Telegram that he was canceling all sports, cultural and other public events in Moscow this weekend.