At least 12 people were killed and 21 injured in a chemical explosion at a factory in Hapur, a district in northern India's Uttar Pradesh, on Saturday, a police official said.

The accident happened at an industrial facility in Dhaulana, about 60 kilometers from capital New Delhi, police spokesman Surendra Singh said.

"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," Indian Prime Minister Narendra Modi tweeted.

Rescue operations are ongoing.

(With input from Reuters)