A massive rescue operation was underway, and by late evening, bodies of five men and a pregnant woman had been recovered from the debris, they said.
The seven-storey building in Shil Dhaigar locality was unauthorised, civic officials said, adding that it was occupied up to at least the fourth floor. The incident took place at around 6.30 PM.
Deputy Collector Manoj Gohad said several persons could still be trapped under the debris.
The injured have been shifted to various hospitals in the city.