Ten fire engines and around 70 firefighters tackled a fire at a nursery with flats above on Green Dragon Lane in Winchmore Hill.
The first floor and the loft conversion were destroyed by fire. Six adults and 18 children safely left the nursery before the Brigade arrived. A further woman also left the property from a flat above the nursery.
Station Commander Darren McTernan, who was at the scene, said: "Thankfully, there were no reports of any injuries.
"On arrival, crews were met with a well-developed fire to the rear of the property which had spread to the loft. Crews worked incredibly hard in hot, difficult conditions to bring the fire under control.
"The fire was producing smoke in the local area and while we know it was difficult on a hot day, we advised people to keep windows and doors closed where possible.
"The junction by Ridge Avenue and Green Dragon Lane was closed, so we asked people to avoid the area throughout the evening."
The fire is believed to have been accidental and caused by self-heating textiles.
A London Fire Brigade spokesperson said: "These types of fires often involve textiles that become contaminated with oil, most commonly linseed, massage and cooking oil on tea towels, tablecloths and chef whites. Make sure you check the manufacturer's cleaning recommendations of your textiles before washing.
"Sometimes when materials are cleaned and put in tumble dryers, the heat from the tumble drying cannot escape. This can result in a high enough temperature allowing it to build up to a point where it smoulders and eventually ignites.
"If you are washing and then drying on a hot cycle, always use the cooling cycle on the tumble dryer so it cools down and allow the heat to dissipate properly, before stacking laundered items together.”
The Brigade's 999 Control Officers took 15 calls to the blaze.
The Brigade was called at 1525 and the fire was under control by 1729. Fire crews from Southgate, Edmonton, Enfield and surrounding fire stations attended the scene.