A Bangladeshi teenager who died in a garment factory that supplies cheap jeans for export to Europe was "overworked to death", a rights group said.

Fatema Akter, 18, a garment worker in the port city of Chittagong, died during her shift in December last year, the US-based National Labor Committee said.

"Forced to work 13 to 15 hours a day, seven days a week, Fatema was sick and exhausted, with pains in her chest and arms," the report said.

Her job was to clean 90 to 100 pairs of finished jeans an hour, it said.

"Rather than grant her a sick day [her supervisor] slapped her face very hard and ordered her to continue working."