Footage shows people taking cover inside the venue as multiple shots are heard
Dozens are feared dead after a gun attack at a concert hall near Moscow, Russian media say.
At least four people dressed in camouflage opened fire at the Crocus City Hall in Krasnogorsk, social media video verified by the BBC shows.
The roof of the concert hall, where people were waiting to see a rock band, is engulfed in fire and collapsing, according to Russia's state news.
Russia's Foreign Ministry described the incident as a "terrorist attack".
Specialist police are at the scene.
Footage on social media shows gunmen inside the hall, and Russian media report that some people are still inside.
Tass news agency says a third of the concert venue is on fire and the roof is almost completely ablaze.
Russian Foreign Ministry spokeswoman Maria Zakharova called on the international community to condemn the incident, which it called "a monstrous crime".
Russian media report that 6,200 tickets had been sold for the concert where the band Picnic was due to perform.
Eyewitnesses have started to speak to Russian media about the attack. One man, called Vitaly, said he was on a balcony in the hall when he heard shots fired.
"We didn't know what happened at first. Then I saw some terrorists shooting people," he said.
"They threw some petrol bombs, everything started burning. We were led out towards an exit."
An anonymous eyewitness said parents were attending a ballroom dancing competition in the venue with their children when the shooting started.
"Children and teenagers were at the competition. People came and said there was shooting. A crush ensued. The children were running out in their ballroom gowns."
Footage shows gunmen in the lobby of the Crocus Concert Hall
US National Security Council spokesman John Kirby said the images of the shooting were "horrible and hard to watch".
