A police officer at the scene said most of the victims died inside their vehicles while waiting to enter Khalis, about 80 km (50 miles) north of Baghdad.
Islamic State suicide bomber kills at least 15 in Baghdad
"We still have charred bodies inside many vehicles including a minibus packed with women and children," the police captain said, requesting anonymity.
There was no immediate claim of responsibility, but Islamic State militants have stepped up attacks even as they incur battlefield setbacks in northern and western Iraq.
Hospital sources said the death toll was expected to rise given the extent of critical injuries.
Amid mourning: Baghdad bombing toll goes up to 213
Iraqi Prime Minister Haider al-Abadi has come under pressure to improve security since a suicide attack claimed by Islamic State earlier this month killed 292 people in central Baghdad, one of the largest attacks of its kind since the U.S.-led invasion in 2003.
The ultra-hardline militants have lost much of the territory they seized in 2014 and Abadi has pledged to retake this year the northern city of Mosul, the group's de facto capital in Iraq.
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