A blast ripped through an illegal firework manufacturing unit at a village near here on Friday morning, killing four workers and damaging several homes and trees nearby.

The brick-walled factory with a roof made of corrugated sheet was completely destroyed in the blast at Devok-Mathpara village which, according to police, has around 250 unauthorised cracker units.

Sources said tremors of the blast were felt even 5km away.

“Three fire tenders controlled the blaze after one hour,” said a police officer, adding that four bodies were found on the site.

“Five workers with critical burns were admitted to Naihati State General Hospital. Another worker is battling for life at Jawaharlal Nehru Hospital in Kalyani,” the officer said.

Two of the dead were females. The deceased were Brinda Sanpui, 40, Kalpana Halder, 42, Mansur Piyada, 17, and Ram Besra, 45.

Kamal Kanti Pandey, divisional fire officer of North 24-Parganas, said: “The reason behind the blast could not be ascertained immediately. But it appears there was a huge stock of explosive chemicals for manufacturing firecrackers.”

Police sources said presence of large amounts of gunpowder and sulphur — used in the manufacture of sparklers and ‘rocket’ firecrackers — might have made the impact of the explosion much stronger.

The police have begun a probe against the owner of the workshop, Noor Islam. “A large police team has been deployed in the area which has been barricaded. A heavy rain hampered the investigation,” the police officer said.

A tree and a portion of the factory damaged in the explosion at Devok-Mathpara on Friday

Barrackpore police commissioner Manoj Kumar Verma said forensic experts had been asked to join the probe and identify the explosives.

The police sources have said Devok-Mathpara in Mahmudpur panchayat has over 250 unauthorised household fireworks manufacturing units. The area is around 8km from here.

Barrackpore BJP MP Arjun Singh, who visited the spot later on Friday, demanded a high-level inquiry into the explosion. “The impact of the blast indicates that there were strong explosives like those which went off at Khagragarh (in Burdwan). Police here

suppress the truth. I strongly suspect there was a deeper conspiracy and have appealed to the Union home ministry

to conduct a high-level probe by engaging the NIA,” Singh said.

Local sources said the blast had occurred about 11.30am when 10 labourers were at the factory.

Haider Mandal, a villager, said: “I heard a huge bang around 500m away. I fell on the ground. Then, I saw a ball of flame rise up in the sky.”

Zafarul Alam, another resident of the area, said: “I felt an earthquake-like tremor and suddenly saw trees catching fire.”

The police said local people continued to carry on with the illegal manufacturing of fireworks despite frequent raids. “We even offered them alternatives employment in the past, but they didn’t accept it,” said a police officer.

A similar explosion at Devok-Mathpara in 2014 had killed a teenage girl.

“These people don’t apply for licences and conduct the trade using political clout. There is nothing we can do other than routine raids,” said the officer.

Zafar Ali, a local youth, said: “It is not possible for us to leave the trade. Over 1,000 people are involved in the firework manufacturing and police cannot feed them. Any occupation has its hazards. So, we take it in our stride.”