More than 100 firefighters are tackling a blaze at an industrial estate.
Crews were called to Long Drive, Northolt, north-west London at around 11.30pm on Monday and multiple units are alight.
London Fire Brigade said 15 engines were sent to the area.
Station manager Ben King said: “This is a very visible fire.
“We would advise nearby residents to keep their windows closed as there is a lot of thick smoke in the area.
“We have a lot of fire engines on the scene so people should avoid the area where possible.”
A third of the building in Northolt is alight (London Fire Brigade/PA)
The cause of the fire is currently not known.
Firefighters are expected to be at the scene for most of the night, and around a third of the building is alight.
Mr King said: “Crews are working hard to prevent the fire spreading to other units. We are likely to be on scene for a number of hours.”
At 3.30am, London Fire Brigade said additional crews were sent to the fire, bringing the total number of firefighters to 120.