Around 50 people were trapped for hours in a four-storey building on Premchand Boral Street near Bowbazar when its main staircase collapsed on Sunday evening.
People on the upper floors, including women and children, had to climb down ladders and ropes from the terrace of the building.
Rescue teams said nobody was seriously injured.
Satyendranath Dey, councillor of ward number 48, said the civic corporation had declared the building dangerous two years ago.
The building houses nearly 30 families.
Police said the staircase leading to the first floor gave way around 7.30pm.
“There were around 50 people on the three storeys above the ground floor. We were trapped and we panicked. We rushed to the roof following instruction from rescue officials,” said Alpana Das, who had to be hospitalised.
An officer said police personnel, fire brigade officials, disaster management volunteers and local residents helped rescue the trapped residents of the building.