Firefighters recovered the bodies of five men and a woman from the top floor of a factory in Muktarpur, about 50 kilometres south of Dhaka, where it appeared they were trapped by the blaze.
"So far we have found six bodies. The search is ongoing," Mustafizur Rahman, deputy district police chief, told AFP.
Police said welders could have sparked the fire, which started in a chemicals storage room inside the four-storey factory.
Fires are common in Bangladeshi clothing factories, despite efforts by the government and international buyers to improve notoriously poor working conditions.
At least 25 dead in Bangladesh factory fire
In July a fire triggered by a boiler explosion killed 13 people and injured 50 more at a factory in Gazipur, an industrial district just north of the capital Dhaka.
Last September, nearly 40 people were killed and 70 injured after a huge fire swept a packaging factory in the same district.
In April 2013, the nine-storey Rana Plaza factory complex collapsed, killing more than 1,100 people in one of the worst industrial disasters in recent times.
Bangladesh has more than 4,500 garment factories, employing four million mostly female workers. The sector accounts for 80 per cent of Bangladesh's more than $35 billion exports last year.
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