Polls opened at 0600 GMT and will close at 2200 GMT, and early figures from the Interior Ministry put nationwide turnout at 19.4 percent, above the 14.9 percent from the same point in 2013, when however the country voted over two days.
The numbers are in line with those from the same point of the constitutional reform referendum in December 2016, when overall 65.5 percent of the nation voted. That would put turnout at the lowest levels for a general
election since the Second World War.
Confusion and delays blighted voting at some polling stations, with new anti-electoral fraud procedures being blamed for huge queues, while in one polling station in Rome voting had to be suspended due to the discovery of voting cards with the wrong candidates' names printed on them.
Tensions between far-right and anti-fascist activists have marred a gloomy campaign dominated by fears about immigration and economic malaise.
"This election campaign has been pretty squalid, including from the Democratic Party (PD), who I voted for," 24-year-old barber Mirko Canali told AFP after casting his vote in Rome.
He said he knew many other young people who, fed up with high youth unemployment, had decided to support the anti-establishment Five Star Movement (M5S).
"They're pissed off, can't bear (PD leader Matteo) Renzi anymore and maybe they're right," Canali said.
Many Italians are cynical about promises made by the many squabbling parties and confused about what the outcome might be.
"I voted for the right and Berlusconi in the past ... but this time I'm voting M5S to be against the parties that have always stolen," said 24-year-old pastry chef Francesco Tagliavini at a polling station in Rome's Tor Marancia neighbourhood.
The result could be a stalemate between the M5S, three-time former prime minister Berlusconi's right-wing coalition and the ruling centre-left PD. The final opinion polls put the coalition in the lead with 37 percent,
followed by the M5S on 28 percent and the centre-left 27 percent.
But under a new electoral law being tried out for the first time, any grouping would need at least 40 percent of the vote to command an overall majority of seats in both chambers of parliament.
A remarkable feature of the election has been the return to the limelight of 81-year-old Berlusconi, despite a political career overshadowed by sex scandals and legal woes.
The billionaire tycoon, who can't hold office because of a tax fraud conviction and has put forward European Parliament President Antonio Tajani as his prime ministerial nominee, was ambushed as he cast his vote in Milan by a topless woman from the Femen activists group who had "Berlusconi, you have expired" scrawled across her body.
Berlusconi isn't just being challenged by the public however, as his plans face opposition from his ambitious coalition partner, League leader Matteo Salvini, whose anti-immigration and euro-sceptic rhetoric has fired up the campaign.
Salvini has said he should be nominated prime minister if his party comes ahead of Berlusconi's and their coalition as a whole wins a majority.
Berlusconi and Salvini have promised to expel 600,000 illegal migrants if they win -- a proposal dismissed by the centre-left as logistically impossible.
The election has drawn international attention, including from former White House adviser Steve Bannon -- the man who harnessed the populist insurgency that propelled Donald Trump to power.
Bannon, who is visiting Italy as part of a European tour, told the paper: "The Italian people have gone farther, in a shorter period of time, than the British did for Brexit and the Americans did for Trump".
He called a potential alliance between the Five Star Movement and the League -- a scenario that has spooked financial markets and European capitals -- the "ultimate dream".
PD leader Renzi told a final campaign event in his native Florence on Friday that only a vote for his party would prevent Salvini from taking power.
"The PD is the only serious political force that can bring concrete results," Chiara Serdone, a 70-year-old retired railway company employee, told AFP at the rally.
If no party wins an overall majority, one scenario outlined by analysts could be a grand coalition between the PD and Forza Italia -- a prospect that would reassure investors but risks spreading more cynicism and emboldening populists and the far-right.
Another possibility could be a temporary government and eventually a new election. The M5S may end up as the single biggest party but has ruled out any post-election deals with the others.
Five Star's leader Luigi Di Maio broke with tradition by announcing a full list of ministerial nominees ahead of the vote, including many academics with no political experience.
The 31-year-old Di Maio told supporters: "Some people have mocked this decision but we will be the ones laughing on Monday.