The boys, two sets of twins, aged 3 and 4 years old, were brought out of the house on Thursday evening and “given immediate CPR by firefighters at the scene,” according to a statement from London Fire Brigade (LFB).
Firefighters found no one in the mid-terrace house besides the children, LFB told CNN.
The boys were then taken to two hospitals, where they were pronounced dead, a statement from the Metropolitan Police said.
Eight fire trucks and around 60 firefighters were called to the fire and faced with “an intense blaze throughout the whole of the ground floor,” LFB said.
The fire service was called at 6:55 p.m. local time, and the fire was under control by 8:36 p.m., LFB said, adding that the cause of the blaze was under investigation.
London Fire Commissioner Andy Roe said in a statement: “This is an incident that has left everyone numb with profound sadness. My thoughts are with the family and friends of the children, the whole local community and all those who will be affected by this fire.
“Fire crews arrived quickly and located 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 counselling as a priority.”