Four people were killed and several others injured in a blast at an illegal firecracker factory in West Bengal's North 24 Parganas district on Sunday morning, police said.

The explosion happened when several people were working at the factory in Nilgunj's Moshpole in Duttapukur police station area, around 30 km north of Kolkata, they said.

Among those injured were many women and children, they added.

The impact of the blast was such that not only did the house where the factory was operating turn into a heap of rubble, but some neighbouring concrete houses were also damaged.

Police said they suspect that several people are still stuck under the rubble.

Rescue and relief work are underway in the area, and firefighters are working to douse the blaze that broke out as a result of the explosion, they said.

A huge contingent of police and personnel of the disaster management department are also at the spot, they added.

Twelve people were killed in a similar explosion at an illegal firecracker factory in Purba Medinipur district's Egra in May.

Leader of Opposition Suvendu Adhikari of the BJP alleged that the state has turned into the storehouse of powder kegs.

"There is no monitoring of illegal activities by the police. These firework units are patronised by local TMC leaders," he alleged.

TMC Rajya Sabha MP Santanu Sen told PTI that the state government has formed a SIT (Special Investigation Team), which busted several such illegal firework units in the last few months.

"If there are some units still functioning illegally, those will also be busted soon," he said.

Sen said that at times action against such firework units also invites the ire of locals as thousands of people depend on them for livelihood. "But we are firm in wiping out the menace of illegal fireworks." Locals ransacked the house of one of the owners of the Duttapukur factory following the blast.

The chairman of firework makers' association 'Sara Bangla Atash Bazi Unnayan Samity' Babla Roy said banned high-decibel 'chocolate bombs' or firecrackers were being manufactured at the illegal factory.

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