The boys, two sets of twins aged 3 and 4, were brought out of the house on Thursday night and “immediately released CPR by firefighters on the scene,” according to a statement from the London Fire Brigade (LFB).
Firefighters found no one in the house in the center of the patio other than the children, LFB told CNN.
The boys were then taken to two hospitals where they were pronounced dead, a Metropolitan Police statement said.
Eight fire trucks and about 60 firefighters were called to the fire and faced “an intense fire throughout the ground floor,” the LFB said.
The fire department was called at 6:55 p.m. local time and the fire was under control at 8:36 p.m., the LFB said, adding that the cause of the fire was under investigation.
London Fire Commissioner Andy Roe said in a statement: “This is an incident that has left everyone emotionless with deep grief. My thoughts go out to the children’s family and friends, the whole community and all those who will be affected by this fire.
“Firefighters arrived quickly and found the children inside the property,” he added. “They were brought out of the house and given immediate emergency care. The welfare of our staff involved in this incident is very important to us and all of them will be offered counseling as a priority.”