Families fled a converted Victorian house after it began to collapse as they slept in the early hours of Sunday.
The foundations of the large semi-detached building dramatically gave way at about 2am, forcing occupants of two flats to escape onto the street to safety.
Neighbours said work had been carried out at the property, in Stanhope Avenue, Finchley, for the past two to three weeks.
A couple in the downstairs flat, including a woman who is seven months pregnant, and a couple upstairs with a young child, all escaped unhurt.
Barnet Council’s building control department is planning a demolition of the damaged flats before surveying the neighbouring buildings.
One contractor said the building could still collapse at any minute and that it shifted at least three inches more this morning.
Witnesses said builders creating a basement underneath the flats pulled out “up to 60 skips of dirt and rubble” in recent weeks.
Pratish Kumar, 50, who lives over the road, was woken by the noise of the building collapsing.
He said: “I just heard this sharp rumbling sound. I thought someone had crashed into the pile of rubble at the front of the house.
“When I next looked out of the window the emergency services were all there. It’s incredible - it looks like a land slip or something.
“It is upsetting for the families, especially those living next door who have been forced out of their homes.”
Police, paramedics and firefighters all attended the incident and evacuated three surrounding properties.
Stanhope Road remains closed to cars this afternoon and building contractors have installed a large fence around two pairs of semi-detached homes.
One family in the house attached to the collapsed building were allowed in to collect some belongings this afternoon.
Neighbours in three adjacent buildings though have been evacuated indefinitely.
Do you live in the flats or have you been affected by the building collapse? Contact the newsdesk on 07824530136 or email email@example.com.