Tuesday's fire broke out in a two-story unit of the Aswad Composite Mills Ltd. factory in the Gazipur industrial area, about 35 miles north of Dhaka, Bangladesh's capital, The Wall Street Journal reported.
The fire was still burning in parts of the building early Wednesday, fire officials said.
Humayun Kabir, one of the assistant general managers, said the fire began in the knitting section on the first floor, the Dhaka Tribune reported.
Some 140 to 170 employees were working when the fire broke out, Kabir said, adding most of the workers safely left the factory.
Abu Zafar Ahmed, head of the Gazipur Fire Service and Civil Defense Station, said the fire became uncontrollable because of a boiler explosion.
Firefighters declined to estimate how many more bodies were trapped inside the factory, the Dhaka Tribune.
Officials said most of the bodies visible from the outside were nearly burned to ashes. Witnesses and some of the workers said they had seen more bodies inside the building.
Aswad Composite Mills has produced clothes for Western retailers, including Walmart, Hudson's Bay, and Loblaw Cos., the Canadian owner of the Joe Fresh label, the Journal said.
The local administration formed a seven-member investigative committee, which has been asked to submit its report within three days.
In April, the nine-story Rana Plaza in Savar near Dhaka that housed five garment factories, collapsed and killed more than 1,100 people.
In November, a factory fire at Tazreen Fashions in Ashulia killed at least 117 and left scores injured.
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