Polls are open in the three northern provinces that make up the region, as well as disputed areas claimed by the Kurds and the government in Baghdad.

Iraq's prime minister has denounced the referendum as "unconstitutional".

Kurdish leaders say an expected "yes" vote will give them a mandate to start negotiations on secession.

Kurds are the fourth-largest ethnic group in the Middle East but they have never obtained a permanent nation state.

In Iraq, where they make up an estimated 15% to 20% of the population of 37 million, Kurds faced decades of repression before acquiring autonomy in 1991.

Voting in Monday's referendum is open to some 5.2 million Kurds and non-Kurds aged 18 or over who are registered as resident in Kurdish-controlled areas of northern Iraq. Polling stations are expected to close at 18:00 (15:00 GMT).

"We have been waiting 100 years for this day," one man queuing to vote at a school in the Kurdistan Region's capital, Irbil, told Reuters news agency.

"We want to have a state, with God's help. Today is a celebration for all Kurds. God willing, we will say yes, yes to dear Kurdistan."