Police attended a residential premises on Wedge Street, Epping about 2pm this afternoon to effect an arrest as part of an ongoing investigation by Darebin Crime Investigation Unit, Victoria Police say.
It is expected police will be there for some time and the incident is not being treated as terrorism-related.
Once on scene, police spoke to a 26-year-old man who initially exited the house before returning inside.
Police are currently trying to negotiate with the man, who is believed to be armed with a firearm.
Investigators believe there are other people inside the house, however they are not being held against their will.
Police have secured the premises and surrounding area, and road diversions are in place.
There is no risk to the general public.
