Many of the 25 million eligible voters were expected to boycott the polls amid deep distrust in a political class widely blamed for graft, unemployment and crumbling public services in oil-rich Iraq.

Prime Minister Mustafa al-Kadhemi's future hangs in the balance, with few observers willing to predict who will come out on top after the lengthy backroom haggling between major factions that usually follows Iraqi elections.

"This is an opportunity for change," the premier said, casting his ballot in Baghdad's fortified Green Zone. "Get out there and vote, change your reality, for Iraq and for your future."

But few shared the enthusiasm, even among those who queued early in the fifth election since the 2003 US-led invasion ousted dictator Saddam Hussein with the promise of bringing freedom and democracy.

"I have come to vote to change the country for the better -- and to change the current leaders, who are incompetent," said housewife Jimand Khalil, 37, one of the first to cast her ballot.

"They made a lot of promises to us but didn't bring us anything."

- 'Corrupt horse-trading' -

The election was held under tight security in a country where the major parliamentary blocs have armed factions and Islamic State group jihadists have launched deadly suicide attacks this year.

Voters were searched twice at the entrance to polling stations and airports are closed until dawn on Monday across Iraq.

The UN and EU sent dozens of election observers.

"Iraqis should have the confidence to vote as they please, in an environment free of pressure, intimidation and threats," said the UN mission in Iraq.

Polls remain open until 6:00 pm (1500 GMT), with preliminary results expected within 24 hours of closing but subsequent negotiations likely to take weeks.

A new single-member constituency system for electing Iraq's 329 lawmakers is supposed to boost independents versus the traditional blocs largely centred on religious, ethnic and clan affiliations.

But many analysts believe the change will be limited.

"The election will likely result in another fragmented parliament, followed by opaque, corrupt horse-trading among factions to form the next government," wrote researchers Bilal Wahab and Calvin Wilder in an analysis published by the Washington Institute.

"Few expect this election to amount to more than a game of musical chairs, and the (protest) movement's core demands -- curbing systemic corruption, creating jobs and holding armed groups accountable -- are unlikely to be met."

- 'We want change' -

The election is being held a year early in a rare concession to the unprecedented youth-led protest movement that broke out in October 2019 in Baghdad and swept across much of the country.

Tens of thousands took to the streets then to vent their rage at corruption, unemployment and crumbling public services, and hundreds lost their lives in protest-related violence.

Dozens more activists have been killed, kidnapped or intimidated since, with accusations that pro-Iran armed groups, many of which are represented in parliament, have been behind the violence.

The movement largely fizzled amid the bloodshed and as the Covid pandemic hit, and the anger has since given way to disillusion among many.

"We want change," said one eligible voter, Mohammed, 23, who asked not to have his full name published.

"I have a degree in Arabic literature but I clean the toilet in a restaurant -- it's humiliating."

Mohammed said he would have liked to vote, but was unable to because he was stuck in the capital and could not make it back to Wassit, his home province, where he is registered.

Observers expect it will take some time for the new balance of power to emerge as the leading factions compete for the support of a larger number of independents.

Iraqi politics are dominated by Muslim Shiite factions, with smaller blocs representing Sunnis, Kurds and other religious and ethnic groups.

The bloc of populist cleric Moqtada Sadr, already the largest in the outgoing parliament, is predicted to make gains but not enough to dominate the Shiite camp.

Sadr, who resisted US occupation but has also criticised Iranian influence in Iraq, voted in one of his strongholds, the Shiite holy city of Najaf in the country's south.

Another major force is the Fatah Alliance, the bloc representing many Iran-backed Shiite armed groups, which is expected to roughly retain its share of seats.