Scotland Yard said the operation was not related to terrorism. Police have set up a tent to cover the scene.
The Met is currently cracking down on gun and knife crime in the capital. A series of raids staged this morning – codenamed Operation Kestrel – involved hundreds of specialist officers, including firearms teams.
There have also been more than 350 firearms-related incidents in the capital so far this year, up 15% on the 2014 figure.