Twelve fire engines and around 80 firefighters have been in attendance at a fire at a recycling yard on Springwell Lane in Harefield.
Around 80 tonnes of scrap metal was alight. The fire is now under control but firefighters have worked through the night to extinguish deep-seat pockets of fire and remaining hotspots. A small number of firefighters remain on scene this morning.
There have been no reports of any injuries.
Station Commander Nathan Beeby, who is at the scene, said: "Working alongside colleagues from Hertfordshire and Buckinghamshire fire & rescue services, crews have been working extremely hard to extinguish this fire, with only deep-seated pockets of fire remaining.
"The fire was producing a large amount of smoke. People in the local area were advised to continue to keep their windows and doors closed at this time due to smoke travel."
Due to the remote location of the fire, one of the Brigade's Hose Laying Vehicles was used in order to increase access to water. Lightweight portable pumps were deployed at the scene.
The Brigade was first notified about this incident at 0941 and Control Officers mobilised crews from Ruislip, Harrow, Hillingdon, Stanmore, Northolt and Barnet fire stations to the scene. Several fire crews from Hertfordshire Fire & Rescue Service have also been in attendance, alongside an appliance from Buckinghamshire Fire & Rescue Service.
The Brigade's drone team were also in attendance, providing the Incident Commander with a greater situational awareness of the fire.
The fire was brought under control by 1316.
The cause of the fire has been recorded as accidental.