The assailant is said to have taken people hostage inside a Citibank office and is demanding a negotiators.
Police have reported the man is threatening to blow himself up, and has an explosive device.
The Russian interior ministry claim the man is holding three of bank’s staff and one customer inside the building in downtown Moscow.
He is said to have initially taken seven people hostage, but let three women go, one after another.
The Russian Investigative Committee have said the man has since released another three hostages, but one remains inside.
Я промок весь насквозь. Будь проклят московский дождь #Москва #захват #банк @moslenta pic.twitter.com/3w9TH0XGTC
— Алексей Коновалов (@KorNew) 24 августа 2016 г.
Police have set up a cordon around the building.
A Rapid Deployment Police Task Force detachment, Russian National Guard units and Federal Security Service (FSB) officers have been deployed to the scene.