The explosion took place at the house in Yaqoobpur town in Bela police station area in the morning, deputy superintendent of police Ashok Kumar Singh said.
A loud explosion was heard after the fire crackers caught fire, killing eight on the spot and injuring 12 others.
The critically injured have been referred to a hospital in Kanpur.
The fire crackers were being illegally manufactured in the house of Motilal and Ram Narain.