An exterior wall on a triplex on De Gaspé Avenue just north of Jarry Street crumbled on Thursday while construction workers were tearing down the neighbouring duplex.
The wall the duplex shared with the triplex came down with the duplex, exposing the inside of the ground-floor apartment.
The triplex was built in 1913.
José Aguiar lives in the building next door. He said he noticed some big cracks develop while the construction crew worked and ran over to ask them to stop.
Three minutes later, the wall came crumbling down.
"It’s incredible. It’s like a nightmare," he said. "You don’t see that every day."
The brickwork on the second-floor apartment fell down as well, but the interior was not exposed.
Neighbours said the wall's collapse sounded like an earthquake.
"Imagine if it would have happened at night. I think he would've fallen out of his bed. The contractor didn't do his job, that's for sure," said Diane Berger, who lives several houses down.
The incident caused minor damage to other neighbouring buildings.