At least 12 people were charred to death and some 20 others injured in a major fire that broke out at a chemical factory in the northern Indian state of Uttar Pradesh on Saturday. Officials said a boiler explosion triggered the fire at the factory located in an industrial area of the state's Hapur district, 80 kms from Delhi, in the afternoon. Within an hour, the blaze engulfed the entire factory. Some 15 fire tenders were pressed into service and it took them a good five hours to completely douse the flames. "As many as 12 bodies, some charred beyond recognition, have been recovered by the firefighters so far. The search and rescue operation is still on," a senior officer of the state fire service said. The victims were all workers of the factory, the fire officer said. Read: Paralysed man charred to death in Ctg fire Hapur range inspector general of police Praveen Kumar, who rushed to the spot within an hour of the fire, said that all the injured were initially taken to a nearby hospital by the local police. "As the condition of some of them worsened, we shifted them to better medical facilities in nearby cities," he told the local media. Local TV channels aired footage of the fire and reported that the impact of the blast was so intense that the roofs of a couple of nearby factories were damaged. Indian Prime Minister Narendra Modi and state Chief Minister Yogi Adityanath took to Twitter to convey their condolences to the bereaved families. "The accident in the chemical factory of Hapur, Uttar Pradesh is heart-wrenching. I express my condolences to the families of those who have lost their lives in this," Modi tweeted. "The state government is actively involved in providing treatment to the injured and all possible help," he wrote. Read: President: 11 babies killed in fire at Senegalese hospital The Chief Minister's office tweeted to say that he "has directed district administration officers to go to the spot and oversee rescue and relief measures and extend all possible help to victims and their families." "A probe has been ordered into the fire," Kumar said. Factory fires are common in India and often attributed to the absence of basic fire safety systems. A number of people die in such fires in India every year.