Four fire engines and around 25 firefighters tackled a fire on Mildmay Park in Islington.
Half of a third-floor self-contained flat, inside a four-storey residential care home, was damaged by fire. One man was treated by London Ambulance Service crews for smoke inhalation.
The fire is being treated as accidental and is believed to have been caused by the unsafe disposal of smoking materials.
A London Fire Brigade spokesperson said: "We'd rather you didn't smoke at all, but if you are a smoker, it's absolutely vital you ensure your cigarette is completely out when you've finished smoking it.
"If you don't, you risk causing a fire which could not only destroy properties but also cost you your life."
The Brigade's 999 Control Officers received five calls about the fire.
The Brigade was called at 2328 and the fire was extinguished by 0026. Crews from Islington, Shoreditch, Holloway and Homerton fire stations attended the scene.
Firefighters' smoking safety tips
· Use proper ashtrays, which can’t tip over and stub cigarettes out properly.
· Don’t leave lit pipes or cigarettes unattended.
· It's safer to smoke outside, but make sure cigarettes are put right out and disposed of properly.
· Don't balance cigars or cigarettes on the edge of an ashtray, or anything else – they can tip and fall as they burn away and cause a fire.
· Take extra care when you’re tired, taking prescription drugs or if you’ve been drinking alcohol.
· Always empty ashtrays carefully. Make sure smoking materials are out, cold and preferably wet them before throwing into a bin – never use a wastepaper basket.