The Special Task Force of Bengal police busted a heroin racket after cops raided the narcotic drug manufacturing unit at Gaihata in North 24-Parganas on Thursday night.

Acting on a tip-off, the Bengal wing of the STF arrested four persons, including two women, who used to run the manufacturing unit.

They also seized heroin in bulk worth around Rs 16 crore in the market, along with raw materials and equipment used to prepare the contraband substance.

"It was a big heroin manufacturing unit and used to supply its produce in various parts of Bengal and possibly Bangladesh. We have arrested four persons, including the chief who is a woman, during the raid. We have seized processed heroin weighing 8kg worth Rs 16 crore along with chemicals and equipment used to process the drug," said a senior STF official.

An official said the arrested persons are Kakali Roy, the alleged chief of the narcotics racket and owner of the two-storey building used to manufacture and process heroin, Doli Sarkar, Tapan Mondal and Abhijit Biswas. All the four persons are residents of Gaighata in North 24-Parganas.

"While carrying out the raid on the house, we learnt that a full-fledged narcotics manufacturing unit was being run secretly on the first floor of the two-storey building. The bedrooms, kitchen and even the washrooms were converted into different sections of the unit to process the drugs," said an official.

A source in the Bengal STF said that after the primary interrogation of those arrested, the cops came to know the unit used to procure raw heroin and then mix chemicals with it to increase the potency and value of the drug.

"We have found a mixer, drier and other equipment that were used to process the heroin. After mixing the raw heroin with multiple chemicals, it used to be dried by using high voltage electric bulbs. The dried material was then weighed and packed in empty plastic packets," said an official.

"Primarily, we came to know that the packaged heroin used to be supplied to various parts of Bengal, including Howrah, North and South 24-Parganas districts. However, we suspect that the racket also used to supply the drug to nearby Bangladesh," he added.

On October 16, the STF busted another heroin racket in Murshidabad district. The STF arrested drug traffickers from Manipur and Nagaland and found heroin worth Rs 1 crore.