Six fire engines and 35 firefighters and officers were called to a fire at a maisonette in Stroud Field, Northolt.
Part of a maisonette was damaged by fire. Two people left the property before the arrival of the Brigade.
A child was treated at the scene by London Ambulance Service crews and one woman was taken to hospital by the LAS suffering from smoke inhalation.
Crews wearing breathing apparatus rescued six dogs and 17 cats from an adjacent property.
The Brigade was called at 1741 and the fire was under control at 1914. Fire crews from Northolt, Wembley, Harrow and Southall fire stations attended the scene.
The cause of the fire is under investigation.