Kirkuk's Kurds had earlier flocked to polling stations, but there has been simmering opposition of the vote among the Arabs and Turkmen who live alongside in the northern Iraqi city.
Voters were asked to say "yes" or "no" to the question: "Do you want the Kurdistan Region and Kurdistani areas outside the (Kurdistan) Region to become an independent country?"
As Iraq's Kurds are rushing headlong into a vote for independence, neighbors and countries in the Middle East, including Iran and Turkey, were trying to persuade the Erbil government to cancel the referendum.
After 2003, Kurdish leaders agreed to an Iraqi constitution that calls for negotiations over disputed areas, so holding the referendum in Kirkuk and other cities now is seen as provocative. CHP to advice gov't on KRG referendum Kılıçdaroğlu, in the meeting, hinted at the CHP's future plans regarding the referendum, saying that in the event that the referendum goes ahead, the main opposition would continue to give advices to the government.
Kirkuk governor Najm Eddine Karim, who was sacked by Baghdad after his provincial council made a decision to take part in the vote, also voted.More news: Commodities - Crude Oil Prices Edge Higher With OPEC Meeting in Focus
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The Kurds are likely to approve the referendum, but they are not expected to result in any immediate declaration of independence.
However, Iran's Foreign Ministry announced on Monday that the country's land border with the Iraqi Kurdistan Region remained open despite its independence referendum. However, it is created to give Masoud Barzani, who heads the Kurdistan Regional Government (KRG), a mandate to negotiate the secession of the oil-producing region.
Iran and Turkey have sizeable Kurdish populations of their own and fear the vote will stoke separatist aspirations at home.
Turkish President Recep Tayyip Erdogan said that Turkish military exercises were happening near the Iraqi border and added that "our military is not (there) for nothing", the AP reported.
The Kurdish region's president, Masoud Barzani, said the night before the vote that "we are ready to pay any price for our independence", according to The Associated Press. "The Kurds are hoping that Iraq will reopen talks", Jane said. "If violence breaks out we are taking a side".