Thick black plumes of smoke billowed into the sky as 80 firefighters tackled a huge blaze at a builders' merchant in Brent Cross on Wednesday.
There was major travel disruption on the roads and trains after 12 fire engines were sent to the scene in Brent Park Road shortly before 4pm.
Video footage and images showed thick plumes of smoke billowing into the sky and blowing across the M1 motorway near Staples Corner.
Transport for London confirmed the motorway was shut between junction 1 and 4 while fire crews tackled the blaze.
Major disruption to trains leaving St Pancras station was also expected to last until at least 7pm, affecting East Midlands Trains and Thameslink routes.
London Fire Brigade said the blaze started at a wood working workshop on the site, believed to be Busy Bee Builders Merchants.
Witness Gavin Ellis was travelling on a train passing the scene of the fire.
He wrote on Twitter: "Train driver just warned us to shut windows as we passed a large fire. Didn't disappoint. #brentcross #fire #smokey"
— Barnet TV (@MyBarnetTV) April 12, 2017
Station Manager Claiton Murray, who was at the scene, said: "This is a large, challenging fire and crews are working extremely hard to bring it under control as quickly as possible. Around half of the workshop is alight. The fire is producing a considerable amount of smoke so we are advising people living and working in the area to keep their windows and doors closed as a precaution."
She added: "The Brigade is working closely with its partners in the Metropolitan Police, London Ambulance Service, the rail network, train companies and Transport for London to bring this incident to a close."
Fire crews from Hendon, Stanmore and West Hampstead fire stations were called to the scene at at 3.45pm.
The cause of the fire is under investigation, but there were no casualties.
Motorists travelling both southbound and northbound have been advised to take a diversion route. For more information from Highways England click here.
Barnet Police took to Twitter to warn of disruption to roads and trains.
National Rail said trains from St Pancras were being cancelled or delayed by up to an hour and that tickets were being accepted on alternative services.
They also said the East Midlands Trains stopper services between Sheffield / Nottingham and London St Pancras would start and terminate at Luton instead.
The fire was brought under control by 9pm thanks to 12 pumps and two aerial platforms, the fire brigade confirmed.
However, disruption remained on the train line between Hendon and Cricklewood, while the M1 was still part-closed at junction 1. Motorists were being warned to check their routes before setting off.