Police have surrounded a house in Lowerhouse Lane, Burnley, and blocked off a road after reports of an incident.
It is believed armed police and dog handlers were called to the terraced property around 4-30pm and specially-trained negotiators are currently trying to make contact with a man inside.
The road was immediately cordoned off to cars and pedestrians from the area outside Lowerhouse Cricket Club through to Sweetclough Drive.
Sgt Phil Turner said: “At the moment all I will say is that we are dealing with an on-going operation.’’
Residents were told to stay indoors while police are dealing with the situation. Neighbours and residents have gathered at the scene as the drama unfolds.