The gas, apparently leaked from two valves and a cracked cylinder of the gas in the cold storage, has spread about a square kilometre area, the sources said.
Panick-stricken residents fled the area, that falls under North 24 Parganas district, after they experienced breathing difficulties and burning sensation in the eyes.
An unspecified number of people, including patients of a nearby private hospital, were evacuated.
A number people of the area fell sick after inhaling the gas and at least ten of them had been admitted to hospitals, official sources said.
However, there was no report of any casualty.
Fire Brigade sources said its personnel had plugged two valves from were the gas was emanating, but the cracks of the cylinder were yet to be detected.
The intensity of the pungent smelling gas had now turned low, they said adding seven fire tenders were pressed into service.
Many people who were in the vicinity of the cold storage meant for preservation of fish were seen wearing masks.
Personnel of the police, BSF, National Disaster Management Group and fire brigade were at the spot to tackle the situation where all shops have been closed and the arterial Jessore Road was stopped near the spot.
Efforts were on to contact the owners of the facility which was closed as it was a Sunday.
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