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 there were 10 to 15 labourers who were working on the tenth floor of the building.
He said that all these labourers had come to work early today so that they could take off on Diwali day.
"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 Mr 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.
In July last year, at least nine labourers were killed when a slab of an under-construction building collapsed in Balewadi area in Pune.