Police have swarmed a public housing apartment block in Carlton amid reports a man with a gun is inside the building.

Officers surrounded the apartment block on Drummond Street about 2.45pm after a witness reported seeing three men, including one who appeared to be holding a firearm, walking into the building.

Police have cordoned off the whole apartment block and several heavily armed specialist police officers were seen entering the building just after 3.30pm.

Other heavily armed officers are also at the scene scouring the outside of the building and front entrance.