Shooting broke out at a large concert hall near Moscow on Friday, Russian news agencies quoted emergency services as saying.
RIA news agency said at least three people in camouflage clothing had opened fire at the Crocus City Hall, and that some people had been wounded.
Police had arrived at the scene, RIA said.
Video footage published on Russian social media channels showed chaotic scenes, with a large crowd of concertgoers attempting to flee the hall, followed by gunshots.
Other video footage showed a number of people lying motionless in pools of blood outside the hall.
Reuters was unable immediately to verify the footage.
TASS news agency reported an explosion and a fire in the building where the shooting took place.
The Kommersant newspaper posted footage online showing smoke billowing from what it said was the concert venue building.
