One explosion ripped through a petrol station in the large northern neighbourhood of Sadr City at around 7:00 pm (1600 GMT), as cars were queueing to fill up, witnesses said.
Motorcyclists, who are not allowed to bring their bikes into the station, were also standing in line with empty jerricans.
"I was on my way to having my mobile fixed at the shop when the car exploded on the other side of the street," irrigation ministry employee Ali Dakhel said.
"There were wounded people shouting and bodies on the ground."
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At least five people were killed, according to hospital and police sources.
Another deadly explosion went off almost simultaneously in the Al-Amin neighbourhood, further east.
"A car bomb exploded at 6:55 pm on the main street in the Al-Amin area," a police colonel said, giving a toll of four killed.
Hospital sources confirmed the figure. A total of at least 32 people were wounded in both explosions.
Fears of a surge in attacks during the ongoing Eid al-Fitr feast marking the end of the holy month of Ramadan have led more people than usual to spend the holiday indoors.