Stunned witnesses watched in horror as scaffolding laden with planks of wood collapsed onto a pavement used by hundreds of schoolchildren every day.
The structure gave way at about 1pm in a busy stretch of Lillie Road in Fulham on Monday afternoon, also spilling into the road. Miraculously, no cars or people were near at the time.
Shopkeeper Balvinder Malhotra heard the incident unfold from his convenience store, Best Quality Food and Wine, and said: "It's a amazing no one was passing - this is one of the busiest roads in the area and is used by hundreds of people a day. There is no doubt this could have killed someone."
Children from nearby schools, including the Bayonne Nursery, Henry Compton and Fulham Cross, use the route.
Mr Malhorta was behind the counter of the store, by the junction of Munster Road, when he heard an almighty crash across the road. "It was a huge bang, you could really feel the power of it," he said.
Another eyewitness, Paul Anderson, said: "I was standing outside smoking and out of the corner of my eye I saw something moving. It seemed to come down in slow motion, the polls were bending 90 degrees and then it crashed to floor.
"If someone had been underneath they would have died, unless they were a very small child. It's really lucky no one was walking down there at the time."
Planning permission was given in June for a three-storey block of flats to built in place of a former council building, which was sold by the authority to Jersey-based firm Golden Dreams Ltd.
Mr Malhorta said building activity on the site had died down recently and that he had been concerned with the safety of the structure for some time.
"It did seem quite overloaded and I have often seen it swaying in the wind," he said. "There have been people working on it every day until a few weeks ago but not so much lately,"
The Chronicle called building firm Alliance Contracting and asked it for comment but its boss slammed the phone down on our reporter, having told him to 'ask the council'.
The authority's investigators are trying to establish the cause of the potentially deadly collapse, but sources indicated a combination of weight and wind are suspected.