Motorists are advised to avoid the area as the road is closed off in both directions between the Wood End Lane junction and the A312 Pett's Hill junction and Dorchester Road.
Video footage taken by @ImYoungSoul shows a number of police vehicles at the scene of what has been referred to as a police incident.
Families have been evacuated from homes in and around Wood End Lane, Northolt after reports a man has barricaded himself inside a property with 'hazardous items'.
Meanwhile there have been several reports on social media site Twitter of police officers swarming in the area around Northolt Leisure Centre.
Other people have reported a possible 'bomb scare'.
One person has said they saw police gathering at Northolt Fire Station just after 7am this morning.
A number of bus routes have been placed on diversion including the 487 and 398 routes, while emergency services deal with the incident.
Local resident Mark Freeman told getwestlondon there were five police vans and ambulance in attendance from around 10.30pm on Friday (October 21) night.
The police incident in Northolt is not affecting the tube stations.
We will update you with more information as we get it.
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