The fire, which engulfed Metatex Chemical factory in Site Industrial area, broke out around 12:30 am local time. It also spread to adjacent buildings, Geo News reported.
Fire tenders from across the city were called in to douse the blaze.
Many blasts were reported intermittently in the building due to storage of chemical while several parts of it were collapsed, the report said.
It said the teams of Pakistan Air Force and Karachi Port also took part in the rescue operation.
Fire-fighting officials declared the blaze a third degree inferno.
Electricity to the surrounding localities was suspended after the factory caught fire, the report said, adding no loss of life was reported in the blaze.