Four fire engines and around 25 firefighters tackled a flat fire on Artisan Place in Harrow.
Half of a ground-floor flat was damaged by fire. Four people left the property before the Brigade arrived and were taken to hospital by London Ambulance Service crews.
The Brigade’s Control Officers took the first of seven calls to the fire at 0220 and sent crews from Harrow, Stanmore and Northolt fire stations to the scene. The fire was under control by 0335.
The cause of the fire is under investigation.