At least 12 workers died and 21 were injured when a boiler exploded at a factory in western Uttar Pradesh's Hapur district on Saturday afternoon, officials said.

There were around 30 people in the affected area at the factory in the UPSIDC industrial area in Dholana, around 80 km from the national capital, when the incident occurred, they said.

The impact of the explosion was so intense that the roofs of some of the factories located in the vicinity were damaged. It took three hours for fire tenders to douse the blaze.

Superintendent of Police of Hapur Deepak Bhuker said 12 people had died and 21 were injured and undergoing treatment.

"The factory was given the licence to manufacture electronic items. And now, it is a matter of probe what exactly was going on here. This is a sad incident. Forensic teams have reached here and are collecting samples," District Magistrate of Hapur Medha Roopam said.

"Our efforts are to ensure that the injured persons get the best medical treatment. Some of them have been referred to Safdarjung Hospital," she added.

Other factories in the area will be inspected, the district magistrate said, adding that action would also be taken against officials concerned if it was found in the probe that the incident took place due to their laxity.

The factory is located adjacent to a CNG pump. Rescue and relief measures were taken up at the site, according to officials.

President Ram Nath Kovind, Prime Minister Narendra Modi and Uttar Pradesh Chief Minister Yogi Adityanath expressed grief over the loss of lives.

"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. The state government is actively involved in providing treatment to the injured and all possible help," Modi tweeted.

"Deeply saddened to hear about the death of many people due to an accident in a factory in Hapur, Uttar Pradesh. I express my condolences to the families of the deceased and wish the injured a speedy recovery," Kovind said in a tweet in Hindi.

The chief minister directed that the incident be probed by experts.

In a statement issued in Lucknow, Adityanath asked the district administration to extend all possible help to the kin of the deceased and injured.

He also said that necessary treatment should be provided to the injured.

The divisional commissioner of Meerut and the inspector general were directed to visit the site and ensure effective implementation of relief work.

"May God give peace to the departed souls and strength to the bereaved families to bear the immense loss. I wish a speedy recovery to the injured," Uttar Pradesh minister for industrial development Nand Gopal Gupta 'Nandi' tweeted.