Part of the roof and the basement of the building were alight. The entire extraction system from the basement level to the roof was also alight.
Station Commander Nathan Hobson, who was at the scene, said: “The fire had travelled via the extraction system to the roof of the building and crews worked swiftly to bring the fire under control.
“Seven people left the building before the Brigade arrived.
“High Road is closed whilst crews continue to work to make the scene safe and we urge people to avoid the area.
“There was smoke in the area and local residents were encouraged to keep their windows and doors closed.”
The Brigade’s 999 Control Officers took nine calls to the blaze.
The Brigade was called at 6.04pm and the fire was under control by 8.39pm. Fire crews from Tottenham, Hornsey, Southgate, Edmonton and surrounding fire stations attended the scene.
The cause of the fire is under investigation.