The London Fire Department (LFB) has tweeted: ""The firefighters are working hard to face a fire after a gas explosion in a three-story block of flats in Fulbeck Way, Harrow."
Ten firefighters and approximately 70 firefighters were called to the scene.
Firefighters using an aerial ladder platform and breathing apparatus rescued a man, a woman and a baby on the first floor.
They were evaluated at the scene and taken to the hospital by the teams of the London Ambulance Service.
An LFB spokeswoman told Express.co.uk: "The incident is ongoing."
The Brigade has reported that the first floor of the house is on fire and the first floor has collapsed.
Approximately 40 nearby residents of the neighboring properties have been evacuated as a precautionary measure since several teams of firefighters attend the dangerous event.
The exact cause of the explosion is not yet clear, but the LFB has said it suspects it was a gas leak.
A statement from LFB said: "The first floor is currently illuminated and has partially collapsed.
"A cord of 20 meters was placed and about 40 people from neighboring properties were evacuated as a precaution.
"They called the Brigade at 0057 and fire crews from Harrow, Northolt, Stanmore and the surrounding fire stations are attending the incident.
"The cause of the explosion is not known at this time, but a gas explosion is suspected."
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