There is a report of hazardous items inside the property
Police in London say an area has been cordoned off after a report of hazardous items inside a property.
Officers attended an address in Wood End Lane at Northolt at shortly after 12:50am on Friday.
The Metropolitan Police say due to concerns for safety of a man at the address and the responding officers, they did not attempt to access the property.
Police cordons are in place, at a 200 metre radius, to facilitate "an ongoing operation".
Armed officers and negotiators are also at the scene.
The police say that some 80 people have been temporarily moved from the area for safety reasons.
"At this stage police believe there is one man inside the address. Whilst it is not known what the man has inside the property, police are treating seriously reports that the items could be dangerous and that attempts have been made by the man to prevent access to the address", Met Police say in a statement.
There is no suggestion the incident is terror-related, and it is not linked to any other ongoing investigation or operation.