Up to 40 people dead after gunfire and explosions in Moscow

Up to 40 people have died and dozens more are injured after a shooting in Moscow. The attack took place at Crocus City Music Hall where several people dressed in combat fatigues opened fire and detonated explosives. The building is on fire and part of the roof has reportedly collapsed. The riot squad and around 50 ambulances have been dispatched to the scene. Moscow's mayor has called the incident a "great tragedy."