Italians go to the polls on Sunday and Monday in an unpredictable election that has pitted mainstream parties against a powerful anti-establishment force, and which observers fear could send the country into a period of political stalemate.

In a contest watched closely by the markets, the centre-left Democratic party (PD) led by Pier Luigi Bersani has been vying with the centre-right Freedom People party of former prime minister Silvio Berlusconi for the lion's share of the vote.

The centre-left bloc was about six points ahead of the 76-year-old billionaire tycoon, who has renewed his alliance with the rightwing Northern League, in the last official poll two weeks ago.

Berlusconi's campaign, boosted by rounds of television and radio interviews, has seen him offer numerous eye-catching measures, such as a property tax refund worth €4bn.

But perhaps the biggest unknown factor in the results is how well the Five Star Movement (M5S), led by former comedian and blogger Beppe Grillo, performs at the ballot box. His campaign, which has filled piazzas throughout the country, most dramatically on Friday night in Rome, has emerged as a powerful draw for voters who are disillusioned and angry with the status quo.

A centrist bloc led by the outgoing technocrat prime minister, Mario Monti, has been languishing in fourth place in the polls. While for some time the scenario deemed most likely by observers has been a PD-led government in alliance with Monti, there is some doubt over whether the former European commissioner's grouping will get enough votes to make that a workable option.

The fractured nature of the political landscape and complexities of the electoral system has raised fears that recession-mired Italy, which has had a decade of near-economic stagnation and more than a year of punishing austerity, could end up with a deadlock in which no strong government is possible.

While it appears likely the PD will achieve a majority in the lower house, the fate of the upper house, or Senate, is less clear.

Voting will continue until 3pm local time on Monday, and results are expected that evening. Last week, a survey suggested up to 5 million of the 47 million-strong electorate were still undecided about who they should vote for. Voters in three regions, including the powerful and populous Lombardy, will also be choosing a regional government.

On Saturday, as bad weather affected much of the country, the interior minister urged Italians to exercise their right to vote. Berlusconi, despite a campaigning ban imposed in the day before polling, took the opportunity to defend himself against what he said were pernicious magistrates' lies.

"They spread the story in Europe that I was ridiculous, by launching this attack on me with 'bunga bunga' which was a sham based on nothing," he said. Italian magistrates, he added, were "more dangerous than the Sicilian mafia".