Two others rescued from the demolished house including an 11-year-old boy were taken to hospital with life-changing injuries.
A further person was treated at the scene after the terraced house was razed to the ground at around 7am amid a blast that sent debris flying hundreds of feet into the air.
The Fire Brigade’s Deputy Assistant Commissioner Richard Welch, from the scene, said: “Firefighters carried out a search of the property and sadly, a child was pronounced dead at the scene.
A resident described the children who lived in the house as “lively” and “happy”.
Maureen Clare, 74, said there were four children and a mother living in the terrace house.
Ms Clare, who lives opposite and was visibly shaken by the incident, said: “They’re very lively kids.
“They were always mischievous, happy and bouncing around.”
Several people, who had been evacuated in their pyjamas, said their windows were shattered early on Monday morning by the force of the explosion which damaged neighbouring properties. The full extent of the devastation can be seen in this drone image by Dan Charity.
The cause of the explosion is being investigated but eyewitnesses spoken to by The Chronicle said they reported a ‘strong gas smell’ in the days before the blast.
Residents on the street told The Chronicle gas works had been taking place for “four weeks” but there is no suggestion the works have any link to the blast at this stage.
Scottish Gas Network (SGN) has been carrying out ‘non specific repairs and maintenance work’ on Galpin’s Road since July 30, according to a permit granted by Merton Council which the house comes under.
A spokesperson for SSGN told The Sun newspaper their engineers are working closely with emergency services to establish the cause of the explosion.
They added: “Following the explosion in Galpin’s Road, Thornton Heath earlier today, our deepest sympathies are with the family of the child who has tragically died as well as those who have been injured.
“We’d like to reassure everyone that our engineers are working closely with the emergency services to establish the cause of the explosion.
“Given the ongoing Police investigation, it is inappropriate to comment any further at this stage.”
In one picture, not far from the devastated house, an area of the pavement and road has clearly been cordoned off with orange barriers by a utility company but there is no confirmation as to who the works belong to.
The Chronicle has asked for a comment from SSGN.
A London Fire Brigade spokeswoman said: “The cause of the explosion is under investigation, we are not in a position to comment at this stage.”
Amongst tragic scenes caught on footage taken in the aftermath of the blast is an image of a man presumed to be the occupant standing on top of “around eight feet of rubble, digging with his hands” as he searched for his partner.
Another resident told how a mum was heard screaming in the street for “my boy” amid the heart-breaking scenes and an eyewitness who lives opposite the explosion said: “I heard a huge boom and when I opened my curtains the whole street was full of smoke.
“Straight away I heard a woman screaming for help. They were still inside the house. Everyone ran out to help her.
“The whole house was completely flattened. There is nothing left of it. It’s just a pile of rubble.
“Windows across the street have been blown out and cars are smashed up.”
Another harrowing picture shows a child’s bedroom gutted by the blast and a toy can be seen on the wall.
Two neighbours, Kutoya Kukanda, 50, and Delroy Simms, 62, said they helped rescue three children from the rubble at around 7am.
But they feared a girl was still trapped inside.
Mr Simms said: “I was getting ready to go to work when I heard the explosion.
“I already knew what it was because that gas was smelling all week, really strong. It was giving me a headache yesterday.
“My neighbour has been calling them (gas engineers) all week. When I heard the explosion it was like an earthquake.
“It shook me up, and my house. The shutters on our windows blew off their hinges. I went to the window and saw the devastation.”
Mr Simms said that Mr Kukanda passed children out to him as bricks were still falling from the structure.
Mr Kukanda, who had a bruise on his shin from a falling brick, said: “I heard boom, then I opened the door.
“I saw smoke, the house had collapsed, and people were screaming inside.
“I went inside and took the first baby – there were three children. I took one of the children, gave it to him (Mr Simms).
“The mother was screaming and saying: ‘One of my daughters is still inside’. Everything was falling.”
Merton Council Leader Ross Garrod said:
“We are all devastated by today’s news about the tragic death of a child as a result of the gas explosion at Galpin’s Road: our thoughts and hearts are with the family affected, and I know everyone in our community will feel the same.
“Residents rightly have questions they want answers to, and a full investigation is underway by the relevant authorities, led by the London Fire Brigade.
“This afternoon we opened an evacuation centre at the New Horizon Centre in Pollards Hill; the council is providing help and support to all those displaced for their homes.
“So far, we have supported around 100 residents at this site, providing food, shelter, water, medicines, wash facilities and housing advice to everyone in need. We are also offering financial support as required. “
An evacuation centre has been established at the New Horizons Centre.