The accident occurred on Monday in Sultanpur district's Jaitapur village and killed six members of a family - Chand Babu (20), Islam (18), Ajay Bheem (20), Mohd Ramzan (12), Mohd Nizam (4) and Mohd Shameen (11), police said.
Five people were severely injured and have been rushed to the trauma centre in the state capital, where their condition continue to be critical.
The unit belonged to Mohd Haneef, who had been in the cracker business for the last five years.
Police said the debris had been cleared. The district administration has ordered a probe into the accident and is verifying if the unit owner had a valid license for manufacturing and stockpiling the crackers.