The blast occurred in a boiler of a chemical factory in the Dhaulana industrial area in Uttar Pradesh’s Hapur on Saturday afternoon, the ANI news agency said.
Police initially reported that eight people died while 15 others were injured, but warned that the death toll could go up as laborers were feared trapped in the fire at the factory.
The Press Trust of India reported later on Saturday that the death toll from the chemical plant explosion had gone up to 12, while the number of injured stood at 21.
Indian Prime Minister Narendra Modi has expressed his condolences to the families of the victims.