Ex-PM Silvio Berlusconi’s right-wing coalition looks set to win the most seats in the lower house of parliament.
It is tipped to get 248-268 seats – below the 316 needed for a majority.
Forming a government may now take weeks of negotiation and coalition-building.
Alternatively, fresh elections could be held in a bid to produce a more decisive result – though there is no guarantee that would happen.
Italian daily newspaper Il Fatto Quotidiano is running a front-page headline saying simply: “Everything will change.”
Though no party will be able to rule alone based on the early poll figures, the surge of support for populist outfits has been compared with Brexit and the election of Donald Trump in the US.
Vote projection figures put the Eurosceptic, anti-establishment Five Star Movement in second place, after the centre-right coalition.
It made significant gains and could emerge as the largest single party in Italy’s lower house, with 216-236 seats.
Public anger over unemployment and immigration appears to have battered the ruling Democratic Party. Its centre-left coalition is projected to come a distant third, with an estimated 107-127 seats.
“It is clear to us that this is a blatant and clear defeat” said Agriculture Minister Maurizio Martina.
Final confirmed results are not expected for several hours. (Courtesy BBC)