"I saw a truck passing through a very narrow road and, a few minutes later, I heard a huge explosion and the ceiling of my shop collapsed on my head," said Akbar Zain al-Abdin, whose fertilizer and farm products store was almost completely destroyed.
"I didn't see a fire, but I saw a huge cloud of sand in the sky. The victims were our relatives and our friends, their houses collapsed on them."
Residents worked with rescue teams to search for people buried under the rubble.
The Turkmen Front, Iraq's main Turkmen political party, announced three days of mourning and called for an "immediate investigation ... and for the criminals to be brought to justice".
|US plans to withdraw its troops from Iraqi cities and major towns by June 30 [AFP]
"The bombing is a big disaster, the criminals and killers chose this time to attack because it is when farmers return home to their houses for lunch," Majeed Azzat, a member of Kirkuk's provincial council, said.
There was no immediate claim of responsibility for the attack.
Kirkuk is plagued by tensions between its Kurdish, Turkmen and Arab communities, which prevented provincial elections from being held there on January 31.
The attack came just days before US forces withdraw from urban areas on June 30.
The authorities have warned that opposition fighters may step up attacks as the security role is transferred fully to Iraqi personnel in an attempt to dent confidence in them.
"Don't lose heart if a breach of security occurs here or there," Nuri al-Maliki, the Iraqi prime minister, told leaders from the ethnic Turkmen community just hours before the attack.
"I, and you, are sure that many don't want us to succeed and celebrate this victory," he said.
"They are getting themselves ready to move in the dark to destabilise the situation, but we will be ready for them, God willing."