The injured were taken to Kirkuk's main hospital, with 30 of them in a serious condition, an AFP news agency reporter says.
As the authorities appealed for blood donors, the reporter met families bereaved by the blast.
Outside the emergency room, a five-year-old boy was crying, saying he had lost both of his parents.
Reskiya Oji, a 49-year-old Turkmen who was wounded in the arm and the leg, said from a hospital bed that her daughter, four, had been killed and she did not know the fate of her two sons.
Rezkar Mahmoud, a 24-year-old Kurd who was wounded in the leg, said he had been having lunch with his father, wife and children.
"The restaurant was full when the bomb exploded," he said. "It sent glass flying and destroyed the walls.
"I don't know where my children and my father are."
At the restaurant, the floor was littered with broken glass and spotted with blood while plates of food and soft drinks cans stood abandoned on tables.
The deputy head of Kirkuk's provincial council, Rebwar Talabani, said the restaurant had been popular with politicians.
"It was packed with people who go there because it's safer [than other restaurants]," he told al-Jazeera TV.
"All kinds of people would go there, even politicians would hold their big meetings there."
The deputy governor of Kirkuk, Saeed Rakan, told the BBC Arabic service that the attack appeared to have been politically motivated.
Children were among the casualties
A Patriotic Union of Kurdistan delegation was meeting councillors from the al-Hawija area, he said, adding: "I think al-Hawija councillors were the target. A number of them sustained light injuries. The bodyguards of al-Hawija council chairman were badly injured."
Although violent incidents in Iraq as a whole have dropped sharply this year, the area around the northern cities of Kirkuk and Mosul remains dangerous, the BBC's Humphrey Hawksley reports from Baghdad.
Tension is so high in Kirkuk that provincial elections planned for most of Iraq next year will not be held in the city, our correspondent adds.
Control of oil-rich Kirkuk is disputed between Iraqi Arabs, Kurds and ethnic Turkmens.
Iraqi Kurds believe they should control the city, which has a Kurdish majority, but it lies outside their semi-autonomous northern enclave.
Ethnic Arabs and Turkmens say it should be under the control of the central government.
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