Iraqis had come to the mortuary to pick up the bodies of relatives for burial, a task which has become an almost daily event, when the car bomb exploded.
Forty bodies with gunshot wounds and some with signs of torture were found in different parts of Baghdad on Monday, an interior ministry source said.
There has been a series of bombings in oil-rich Kirkuk in recent months amid tensions between the Kurdish and Sunni Arab populations.
Kirkuk, north of Baghdad, is disputed by Sunni Arabs, Kurds and Turkmen and its final status is one of Iraq's most contested issues.