Opinion polls suggest that up to eight political parties may enter the next parliament, with the centre-right GERB party of former premier Boyko Borissov leading with about 25 percent of the vote.
Bulgarians have begun casting their ballots in a general election - the fourth in 18 months - marked by a raging war nearby, political instability, and economic hardships in the European Union's poorest member.
Polling stations opened at 7 am local time (0400 GMT) on Sunday.
First exit poll results will be announced after polls close at 8 pm local time (1700 GMT) and preliminary results are expected on Monday.
Surveys ahead of the vote suggest that up to eight parties could muster the 4 percent threshold to enter a fragmented parliament where populist and pro-Russia groups could increase their representation.
Turnout is expected to be low due to voters’ apathy and disillusionment with politicians unable to cobble together a viable government coalition.
The early election comes after a fragile coalition led by pro-Western Prime Minister Kiril Petkov lost a no-confidence vote in June.
He claimed afterward that Moscow used “hybrid war” tactics to bring the government down as it refused to pay gas bills in rubles and ordered a massive expulsion of Russian diplomats from Bulgaria.
GERB party in the lead
A low turnout favours the former ruling GERB party of three-time former Prime Minister Boyko Borissov that despite a further erosion in support can still count on a bulk of loyal voters, and it is likeliest to finish first.
Still, the predicted percentage won’t be enough for Borissov’s party to form a one-party government, and the chances for a GERB-led coalition are slim as it is blamed for corruption by most opponents.
A recent Gallup International survey ranked GERB first with 25.8 percent, followed by its main rival - Kiril Petkov’s We Continue the Change party with 16.6 percent.
Petkov rejected pollster results as questionable and voiced confidence that the vote will yield positive results for his We Continue the Change party.
“This time we will win even more, and I expect that we will be able to form a coalition,” he said at his party’s final campaign rally Friday.
The war in Ukraine was among the main topics in this campaign and calls by the leader of the pro-Russia party Vazrazhdane, Kostadin Kostadinov, for “full neutrality” of Bulgaria in the war, or calls to renegotiate relations with the EU, are attracting many voters.