The incident occurred when a large group of women and children gathered on the balcony of a quarter of the closed National Jute Mill at Banipur under Sankrail police station to watch the Muharram procession.
The balcony collapsed killing Fizora Khatun (35) and injuring 30 others, including six children.
The injured were admitted to several hospitals where the condition of five was stated to be serious, sources said.