At least 13 people were killed and six injured in an explosion at a shop in Bhadohi on Saturday afternoon which led to the collapse of three adjacent houses, officials said.
It is suspected that some people are still trapped under the debris and a rescue operation has been launched, they said.
Chief Minister Yogi Adityanath has expressed grief over the loss of lives in the incident and directed the district officials to ensure proper treatment of the injured, a spokesperson said in Lucknow.
The blast took place at the shop in Rohta Bazaar, which was run by Kaliyar Mansoori. His son was running a carpet factory behind the shop and its workers could be among those trapped under the debris, District Magistrate Rajendra Prasad said.
Locals claimed that Mansoori was also in the business of making illegal firecrackers.
Earlier, four of the deceased were said to have been identified but the identity of all was yet to be verified, the DM said, adding the injured have been admitted to hospital.
Earthmoving equipment has been pressed into service to carry out relief and rescue works. Teams of forensic experts, National Disaster Response Force and senior district officials have reached the site, he said.
Superintendent of Police Rajesh S said SHO of Chauri police station Ajay Kumar Singh, and police chowki in-charge Pramod Kumar Verma have been placed under suspension.