Six fire engines and around 40 firefighters attended a suspected gas explosion on Western Road in Southall.
The first floor and roof of a two-storey building, with a shop and flat above, has suffered significant structural damage as a result of the building partially collapsing. Part of the first floor and loft space was damaged by a fire which occurred following the explosion.
Two men and a woman left the building before firefighters arrived. They have been taken to hospital by London Ambulance Service crews. There were no reports of any other injuries. Neighbouring properties were evacuated as a precaution and road closures are in place.
Station Commander Simon Horn, who was at the scene, said: "Crews were joined by our Urban Search and Rescue team using specialist equipment to carry out a systematic search of the property. They were able to confirm that everyone has been accounted for.
"Initial crews worked quickly in a challenging situation to extinguish the fire. However, a cordon of around 50 metres will remain in place and people are asked to avoid the area."
The Brigade's 999 Control Officers received eight calls about the incident.
The Brigade was called at 1329 and the incident was under control by 1605. Crews from Southall, Feltham and surrounding fire stations attended the scene.
The cause of the incident is under investigation by the Brigade and Metropolitan Police.