Six fire engines and around 40 firefighters were called to a fire behind a row of shops and flats on Lyndhurst Road in Wood Green.
The alarm was raised after a neighbour smelt burning and saw flames at the first floor window. The fire was outside underneath an emergency exit and engulfed the metal stairwell in flames. Three adults and a child were unable to leave the building and remained on the phone to Brigade Control Officers who issued safety advice.
Firefighters wearing breathing apparatus led the four occupants to safety via the external staircase. They were all treated on scene by London Ambulance Service crews for smoke inhalation.
Two fridge-freezers and a photocopier were damaged by the fire.
Crews carried out a home fire safety visit following the blaze and installed smoke alarms in the flats.
Fire crews from Southgate, Hornsey, Holloway and Tottenham fire stations attended.
The Brigade was called at 1803 and the fire was under control by 1917.
The fire is believed to be accidental.