Six fire engines and around 40 firefighters tackled a fire on Holloway Road in Holloway.
A ground floor flat was destroyed by fire. Part of a shop was also damaged by fire along with an office space on the first and second floors of the building. One man was taken to hospital by London Ambulance Service crews. Six people left neighbouring flats before firefighters arrived.
The fire is being treated as accidental and is believed to have been caused by a heat source placed too close to combustible items.
A London Fire Brigade spokesperson said: "The rise in energy costs means there’s a very real risk of heating-related fires. We know that people will turn to alternative ways to keep their families warm overnight without turning on the heating, we just want to make sure that people are staying safe at the same time.
"We know that people may want to use portable heaters to heat just one room. It’s important to follow the manufacturer’s instructions and ensure these items are safety registered and in good working order. If you’re using these items around children always supervise them carefully and place heaters somewhere where they won’t be accidentally knocked over and away from anything that could catch fire."
The Brigade's 999 Control Officers received six calls about the fire.
The Brigade was called at 0345 and the fire was brought under control by 0532. Crews from Holloway, Kentish Town, Stoke Newington and surrounding fire stations attended the scene.