A warehouse was destroyed and several vehicles badly damaged when a huge blaze broke out at an industrial yard near the M25.
The fire, which was tackled by 72 firefighters, began in Whitewebbs Lane in Enfield at about 02:00 GMT.
Drivers were warned to take care as heavy smoke drifted across the M25 between junction 24 and 25.
London Fire Brigade said the blaze was under control but crews remained at the scene "damping down pockets of fire".
Deputy Assistant Commissioner Graham Ellis said it had been "a difficult fire to fight" and firefighters had "worked exceptionally hard".
The cause of the fire is not currently known.
The blaze destroyed a 150m by 100m stack of wooden pallets and burnt down a warehouse.
Eight cars, seven forklift trucks, six lorries and three caravans in the yard were also badly damaged.
Two men staying in a caravan escaped uninjured before the fire brigade arrived.
Firefighters moved 35 propane cylinders from the site but warned others could still be in the vicinity of the blaze.
Highways England earlier tweeted that ash and sparks were drifting towards both carriageways of the motorway.
Whitewebbs Lane, which is currently closed, is the location of Tottenham Hotspur Football Club's state-of-the-art training centre.
The club said that although the road was shut, the centre was still open and running as normal.
Fire crews from Enfield, Edmonton and the surrounding area battled the blaze.