The victims were working on the fourth floor of the building, part of an ayurvedic college, when the cement slab gave way, they said.
More labourers could still be trapped under the debris and efforts were on to rescue them, officials said.
One person was reportedly rescued from the site and admitted to hospital.
Fire Brigade personnel were trying to extricate bodies of the victims from under the debris.
Police said they were probing the reason behind the collapse of the cement slab suspected to be of an inferior quality.
(With PTI inputs)