The apparent razor-thin victory of Pier Luigi Bersani's Democratic Party coalition could make him prime minister and, at best, create a shaky coalition government, but would likely lead to political gridlock and possibly lead to a "hung Parliament," the BBC said.
A hung Parliament is when neither major political party or bloc of allied parties has an absolute majority of parliamentary seats.
The Interior Ministry said the election's margin of victory in both houses was less than 1 percent and in some cases less than 0.5 percent.
Control of both houses is needed to govern and a Berlusconi official said the election was "too close to call."
Angelino Alfano, secretary of Berlusconi's center-right People of Freedom party, called the results "extraordinary" and urged the ministry to wait before declaring a final result.
"It is clear to everyone that a very delicate situation is emerging for the country," Bersani said.
A protest movement led by former comedian Beppe Grillo, who ran with a throw-the-rascals-out platform, won a quarter of the vote in the lower house, or Chamber of Deputies, making it the single-largest party in that house, unofficial results indicated.