At least 21 people were killed and dozens injured in a fire at a garment factory on Friday near Bangladesh's capital.  

Firefighters struggled for hours to put out the blaze, the cause of which was unknown, said a policeman from Dhaka's Siddirganj suburb.

"Twenty-one charred bodies have been recovered from the factory, where dozens of injured were still lying," the policeman said.

Thick smoke from the four-story Sun Knit Garment Factory still hung over the wide area, witnesses said.

Fire officials were investigating the cause of the fire, which destroyed the building.

Bangladesh earns over US$5 billion a year from garment exports. The sector employs about 2 million workers, most of them women. But lax safety standards and poor electrical wiring cause several factory fires every year in Bangladesh, killing dozens of people, police and firefighters say.