Three shanties were damaged in the incident that occured arund 11:30am in Dawari Nagar locality in Santacruz (East).
The injured have been identified as Viraj Paste (15), Santosh Paste (43) and Sanjay Paste (45), a police official said.
A resident of the chawl said he was sitting inside his room when he heard a thud and people screaming.
“We rushed to Paste’s shanty and rushed them to hospital,” he said.
He claimed that an iron rod had fallen from the under-construction 13-storey building in the past.
Another resident demanded registration of an FIR against the builder concerned for the incident.
Mumbai is on alert in view of cyclonic storm ‘Nisarga’ which made landfall near Alibaug coast, about 95 kms from here, around 12:30pm.