Many of the victims were daily labourers waiting for jobs at an intersection in Sadr City, a sprawling majority Shiite neighbourhood in the northeast of the capital that has been repeatedly targeted.
Pictures posted on social media shortly after the explosion showed a huge plume of black smoke billowing into the sky and seriously injured people being evacuated.
According to a police colonel, at least 32 people were killed and 61 wounded in the blast, the second major attack in Baghdad in three days.
There was no immediate claim for today's suicide blast but the Islamic State jihadist group has claimed all such attacks recently, including the double bombing on New Year's Eve.
The caliphate IS proclaimed in 2014 is shrinking steadily and jihadist fighters are defending Mosul, their last major urban stronghold in Iraq.
Observers have voiced fears that the group, once it definitively loses its status as a land-holding force, could increasingly revert to targeting civilians in Iraq's cities.
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