Three armed men opened fire inside the Crocus City Hall concert hall in the Moscow region, according to Russian state media agencies TASS and RIA Novosti.

There are believed to be dead and wounded, Russian state media reported, without specifying any numbers.

“People in camouflage, at least three, burst into the ground floor of the Crocus City Hall and opened fire with automatic weapons,” RIA Novosti reported Friday, citing its correspondent on the scene.

RIA Novosti said the three men “threw a grenade or an incendiary bomb, which started a fire” in the concert hall.

A large plume of black smoke was seen billowing from the burning building, which appeared engulfed in flames, according to video footage from the scene.

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.

More than 50 ambulance teams were sent to Krasnogorsk, a town in the Moscow region, to provide medical care to all those in need, the Moscow Region Ministry of Health told RIA Novosti.

Moscow Mayor Sergei Sobyanin called the incident 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.

This is a developing story and will be updated.