(Express) -- The blast occurred in Finsbury Park, North London, and 10 fire engines and 72 firefighters raced to the scene to quash the flames.
The address has been evacuated, but no neighbouring properties have been affected.
Police have launched an investigation, but have confirmed it was not a terrorist incident. No one has been arrested.
A London Fire Brigade spokeswoman said: "We were called at 12:03 to reports of a fire on Stapleton Hall Road. We now have ten fire engines at the scene."
A London Ambulance Service spokesperson said: "We were called at 12.03pm to Stapleton Hall Road, N4, to reports of an incident.
"We sent a number of ambulance crews including our Hazardous Area Response Team to the scene.
"We also dispatched London's Air Ambulance. We assessed three patients and took two of them to hospital."