A woman working at a Chicago charity shop was killed when a gun that was in dropped-off clothing accidentally discharged, hitting her in the chest.

Chicago police say Carmen Dominguez, 54, and a male co-worker were sorting the donated clothing in a back room of the store in the city's Washington Heights neighbourhood early yesterday when the co-worker shook a sock.

A .22-calibre gun inside the sock fell into the co-worker's hand and discharged.

The wounded woman was taken to a hospital where she was pronounced dead.

Relatives said she was a wife and mother of two children.

The US Occupational Safety and Health Administration is investigating.