Around 2.10 am, the fire engulfed the second floor of the building which housed a cloth manufacturing unit at Haji Ratan Lane in the Metiabruz area.
"We had rescued three people in a conscious state and one with severe burn injuries and rushed them to the SSKM Hospital," a fire station official said.
Fire officials said that they would soon investigate the cause and extent of the fire, including damage to property.
The fire has been put off by now, the official added.