At least 11 people died in eastern India after a massive explosion at a house where firecrackers were being made illegally, officials said Friday.

The impact of the blast, which happened Thursday night, also destroyed four adjoining houses, and the sound was heard 15 kilometres (nine miles) away, said the local magistrate of Bhagalpur district in the eastern Bihar state.

"Eleven people have been killed and five others who are injured are undergoing treatment," Subrat Kumar Sen told AFP.  

Excavators and cranes were clearing huge mounds of debris, with little chance of anyone being still buried, he added.

Prime Minister Narendra Modi offered his condolences for the "painful" loss of life and said the administration was providing all possible assistance in relief and rescue operations.

Explosions are common in illegal firecracker workshops across India, many of which do not adhere to basic safety requirements and operate without permits. 

In 2019, 18 people were killed in an explosion at a firecracker factory in the northern state of Punjab.