Police said at least 221 people were also injured when the vehicles exploded at 7am (0400 GMT) on Tuesday in
A roadside bomb exploded near an Iraqi police patrol an hour and a half later and a third blast rocked the city centre after that.
Witnesses described how a pair of vehicles were involved in what Nuri al-Maliki, the Iraqi prime minister, called "a horrible massacre", referring to the Tayran Square attacks.
First a BMW car rear-ended a police vehicle and exploded, prompting crowds of day labourers and stall holders to take shelter on the other side of the square. Two minutes later, a pick-up truck ploughed into the crowd and exploded.
"After the explosion, not a single person in the square was standing. I thought everyone was dead," said Khaled Nasser, a labourer who searched the wreckage for four of his companions.
"I found them all cut in half, no legs, and for some I could only find their heads."
Two buildings were severely damaged in the blasts and dozens of shops were burned, while plumbing fixtures and tools from vendors' stalls lay scattered through the bloody debris.
"We are treating 25 people with extremely serious injuries," a doctor from Ibn al-Nafis hospital said.
Afterwards, Iraq's Sunni parliamentary speaker described the attackers as "outlaws and without a religion", and called upon all armed groups to observe a truce for two months.
In a statement, Mahmud Mashhadani said: "This massacre shows that those terror groups are endeavouring to create chaos and killing, beside arousing sectarianism in the country.
"Security forces will track down those criminals and arrest them and take them to justice to get the punishment they deserve."
Doctors attend to the casualties of Tuesday's
bombings in Baghdad's Tayran Square
Many Iraqis doubt, however, the security forces' ability to halt the country's rapid slide into lawlessness.
Baghdad is currently the scene of a cycle of revenge attacks between Sunni and Shia groups, with the use of car bombs increasing.
The UN estimates that more than 100 Iraqis are being killed across the country every day, many from sectarian-related attacks.
In other violence, an Iraqi cameraman working with Associated Press Television Network (APTN) was shot dead in the northern city of
"The AP has received word that an APTN cameraman in
At least 127 journalists and media workers have been killed across
Elsewhere five people were killed while police found 13 bodies in Baquba, northeast of