At least six people, reports ndtv.com, including a four-year-old child and a woman, have been killed and four others injured in a massive explosion in an illegal firecracker unit in Bihar's Saran district on Sunday, police said.

The blast was so powerful that the three-storey building in Khodaibag Bazar from which it was operating collapsed, Saran Superintendent of Police Santosh Kumar told reporters.

"Five people, including a four-year-old child and a woman, died on the spot. Four others have been injured. The owner of the house has been identified as Shabir Hussain and he was allegedly running the illegal firecracker unit.

"Operations are underway to rescue trapped persons, if any, from under the debris. We are trying to ascertain the identity of the deceased. Forensic experts have been asked to come from Patna. Further investigation is underway," he added.