“It’s a busy street with restaurants and shops, there is great destruction,” a Kirkuk police colonel said, adding that a suicide car bomb was used.
He said the target of the explosion was a popular cafe called Dawooda in the predominantly Kurdish northern neighbourhood of Shorjah.
Both he and the head of the health directorate for Kirkuk province, Sabah Mohammed Amin, said the blast killed at least 18 people and wounded 22.
In the capital Baghdad, two car bombs went off at around 6:30 pm (1530 GMT) near markets in different parts of the sprawling northern district of Sadr City that are usually bustling with people on Thursday evenings.
At least nine people were killed and 25 wounded in one blast, while at least six died and 22 were hurt in the other, a police colonel and a hospital source said.
The capital is rocked by several blasts a week, including suicide bombings, most of which have lately been claimed by the Islamic State group.
The disputed oil hub of Kirkuk, about 240 kilometres (150 miles) north of Baghdad, is an ethnically mixed city which lies outside the recognised autonomous Kurdish region but is currently under the full control of the Kurdish peshmerga forces.
The last major bomb attack in Kirkuk was in August when triple blasts, including two targeting the Kurdish security forces, left 38 dead.
Violence has increased in the Kirkuk region in recent weeks, as IS fighters are being squeezed out of some of the positions they had held in the east of the country since June. -AFP