A senior police official told UNI that the search operation began by the NDRF using two sniffer dogs this morning.
He said so far nine people, have died in the mishap, which occurred around 11: 50 PM on Sunday in the thickly populated Garden Reach area.
Among the dead, two Shama Begum( 44) and Hasina Khatun( 55) were sisters and two were cousins and masons by profession, who were sleeping on the 2nd floor of the under-construction multi-storied building when it collapsed.
The building was being built for about a year after covering a water body there, local people alleged.
The promoter was arrested.
The construction of the building was illegal and was being built on a 4 ft wide lane.
The lane also has many three or four-storied buildings.
Two side-by-side buildings on Paharpur Road are tilted and the gap is only a few inches on the rooftops, local people alleged.
The Kolkata Municipal Corporation (KMC) already posted a notice about a dangerous building in 2023 but some residents are still staying there.
Meanwhile, the Bidhannagar Municipal Corporation on Tuesday began the demolition of a multi-storied building of a club at Nayapatti in the Salt Lake area.
The demolition order is being carried out following a Calcutta High Court order after the owner of the land filed a writ against the illegal construction, police said.
(With UNI inputs)