Commuters using a key Tube line are facing serious disruption as firefighters tackle a blaze close to the tracks.
London Fire Brigade said the Piccadilly line was expected to be “severely impacted” by the fire in South Harrow.
Transport for London said there would be no service between South Harrow and Uxbridge, with severe delays westbound between South Harrow and Acton Town.
Around 100 firefighters worked to bring the fire in railways arches beneath the tracks under control and the brigade said they were likely to be on the scene near Roxeth Green Avenue into the morning.
A statement from the brigade said the fire was under control and there were no reports of any injuries.
They said businesses within the arches, which include vehicle workshops, had been affected by the fire.
A number of gas cylinders are believed to have exploded, with firefighters removing and cooling two further cylinders.
People living near the scene were advised to keep windows and doors closed at the height of the fire, while road closures were expected to be in place into the morning.
The brigade said 15 fire engines from Harrow, Wembley, Stanmore and Ruislip had been sent to the scene after it received the first calls just after 1.15am on Friday. Two 32-metre turntable ladders were being used to fight the fire from above.
The cause of the fire is being investigated.
