The man remains under arrest and police are continuing to investigate. Officers have had no reports of any injuries.
Police said in a statement: “Police were called at 2.02pm on Monday to Weir Road, SW12 to reports of a man with a firearm.
“Officers attended, along with London Ambulance Service as a precaution, and a man, no further details, has been arrested on suspicion of possession of a firearm with intent.
“He has been taken to a London police station, where he remains. Road closures are in place in the surrounding area.
“Officers remain on scene and inquiries continue. There have been no reports of any injuries.”