Armed police have spent a second night locked in a stand-off with a man who is said to have dangerous items.
Up to 80 people have been evacuated from addresses in the immediate area in west London as a precaution.
Scotland Yard said police were called on Saturday, shortly before 1am, to reports of concerns for an occupant and hazardous articles inside the address at Wood End Lane, Northolt.
Negotiators are at the scene.
Ealing Council leader Julian Bell said officials were working closely with the police to try to deal with the incident.
He said: "The safety of our residents is our top priority and council officers will continue to be on hand to give any necessary assistance until the incident has been resolved."