Many casualties as gunmen open fire at Moscow concert hall

As many as five gunmen dressed in camouflage clothing opened fire with automatic weapons at people in the Crocus City Hall music venue near Moscow, leaving an unknown number of people dead and injured, video footage from the scene showed.

It was not immediately clear how many people had been injured and who the gunmen were, but Russian news agencies said 50 ambulance crews had been sent to the scene.

Flames leaped into the sky and plumes of black smoke rose above the venue, video showed.

"A terrible tragedy occurred in the shopping centre Crocus City today," Moscow Mayor Sergei Sobyanin said.

"I am sorry for the loved ones of the victims."

Sobyanin said all necessary assistance would be provided to those injured during the incident.

Russian rescue services have evacuated about 100 people from the basement of the hall, but there are still people on the roof, Russian news agencies reported

In one unverified video posted on social media, men with automatic weapons were shown firing repeatedly at screaming civilians, including women, who were cowering below what looked like an entrance sign to "Crocus City Hall".

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