Two populist and stridently anti-European Union political groups, both fierce rivals, surged in Italy's parliamentary election at the expense of the country's traditional powers, but neither gained enough support to govern alone, preliminary results showed.
With no faction winning a clear majority in Sunday's vote, a hung Parliament was expected and long, fraught negotiations to form a new coalition government lay ahead.
Financial markets opened lower on Monday on the news and were volatile.
"Ungovernable Italy" headlined the La Stampa newspaper.
Preliminary results released by Italy's Interior Ministry showed the centre-right coalition winning about 37% of the parliamentary vote and the populist 5-Star Movement getting about 32%. The centre-left coalition was far behind with 23% support.
In an upset, the results showed the populist, right-wing and anti-immigrant League party led by Matteo Salvini surpassed the longtime anchor of the centre-right, the Forza Italia party of ex-Premier Silvio Berlusconi. According to the partial results, the League captured around 18% of the vote, while Forza Italia had less than 14%.
A triumphant Mr Salvini celebrated the victory of the centre-right bloc, saying it had won the "right and the duty to govern", and announced that his party, not Mr Berlusconi's, would lead that effort.
Mr Salvini said he would begin sounding out any potential allies to reach the necessary parliamentary majority, but he ruled out any "strange coalitions", an apparent reference to a possible alliance with the 5-Stars.
"I am and will remain a populist," he said. He repeated his belief that joining the common euro currency was a mistake for Italy, but said financial markets should not fear his party's leadership.
But the anti-establishment 5-Stars were the highest vote-getter of any single party, prompting their leader, Luigi Di Maio, to immediately assert his right to govern Italy. Mr Di Maio noted on Monday that no campaign bloc had obtained a majority and that the 5-Stars had strong showings from north to south.
"The fact that we are representative of the entire nation projects us inevitably toward the government of the country," Mr Di Maio said at a news conference in which he took no questions. "Today, for us, it is the start of the Third Republic. And the Third will finally be the republic of citizens."
Monday's results confirmed the surging of populist, right-wing eurosceptic forces that have swept across Europe and the defeat of the two main political forces that have dominated Italian politics for decades, Forza Italia and the centre-left Democrats.
"The vote has radically transformed Italy's political landscape and its repercussions will be long-lasting," said political analyst Wolfango Piccoli.
Mr Piccoli, the co-founder of the Teneo Intelligence consultancy, said the negotiations to form a coalition government would be "prolonged and the outcome uncertain".
Mr Piccoli said the centre-right is best positioned to form a government, expected to secure 250-260 seats in the 630-member lower house. Still it will fall short of the 316 needed to control a majority.
The 5-Stars are expected to get 230 seats.
"The European Union is having a bad evening," French far-right leader Marine Le Pen tweeted. British pro-Brexit campaigner Nigel Farage also congratulated the 5-Stars.
The 5-Star Movement considers itself an internet-based democracy, not a party, and views established political parties as a parasitic caste. Since its birth in 2009, the 5-Stars have attracted legions of mostly young Italians who are facing few job prospects and are fed up with Italy's traditional politicians.
The 5-Stars had a remarkably strong showing in the south, which has long been a stronghold of the centre-right and Forza Italia.
During the campaign, Mr Di Maio backed off early 5-Star policy to push for a referendum to get Italy out of the shared euro-currency group. But 5-Star members, who espouse a range of ideology-defying pro-green, anti-bank views, rail against what they say are excessive EU rules.
"In all these years we have been going against the current. Now we are starting to fly," marvelled Davide Casaleggio of the 5-Stars.
It will now be up to President Sergio Mattarella, a constitutional scholar, to sound out the political parties to determine who has the best chances of forming a government.
The League, which only captured 4% of the national vote in the last general election in 2013, was particularly strong in the north, its traditional base. In Veneto, where it won 11% in 2013, it captured around 33% this time around.
Mr Salvini, who never has held public office in Italy, fed public anger at the EU's inability to help Italy handle the hundreds of thousands of migrants who have flooded into the country after being rescued while crossing the Mediterranean Sea.
He had vowed during the campaign to expel 150,000 migrants in his first year, but said Monday that the League's strong showing was due more to its economic proposals than its anti-migrant stance. The League has proposed overturning pension reforms, introducing a flat tax and cutting bureaucracy.
"While some were doing anti-fascist marches in the absence of fascists, we were preparing the future," Mr Salvini said.
Still the anti-migrant stance proved popular. The League surged to more than 20 percent of the vote in Macerata, where a former League candidate shot six African migrants in the election campaign. The League did not even reach 1% there in 2013.
Between the League and the 5-Stars, the results showed that the two parties with the most eurosceptic platforms together topped the 50% needed to rule Italy. While the two are rivals, if they joined together, analysts have called that a "nightmare scenario" for the European Union and the financial markets.
"No, no, no," Salvini said when asked about the possibility of governing with the 5-Stars.
The election results showed a stunning loss for the Democratic Party, the main partner in the centre-left government that has ruled Italy since 2013. The Democrats received 25% of the vote in 2013.
Agriculture Minister Maurizio Martina called the outcome "a complete defeat."