The deceased have been identified as Prakash Saav (26), Dulari Paswan (28) and Mithun Singh (22), police said, adding, one of the labourer Ramu Paswan sustained injuries.
All of them hail from Jharkhand and died on the spot, said police.
According to police, the site belongs to Pate Developers.
Senior police inspector Anil Patil of Dattawadi police station said that as per the information there were 10 to 15 labourers who were working on the tenth floor of the building.
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"According to the statements given by other labourers, they took an early lunch break and left the floor but four labourers continued working.
"As per the preliminary information, all the four fell off after the platform they were working on collapsed. They were doing the centring work on the tenth floor," said Patil.
Police said they are investigating whether the developer and contractor had adopted all the safety measures for labourers at the site.
"We are investigating the exact cause of mishap and whether the safety measures were taken. We are in the process of registering the case," he said.