Support for PM Boyko Borisov's GERB party has been eroded by a series of scandals, with protests last year accusing the government of protecting oligarchs.
The centre-right GERB party of Bulgarian Prime Minister Boyko Borisov has come first in parliamentary elections with around 25 percent of the vote, according to partial exit polls.
However, the exit polls also suggest that anti-government protest parties did better than expected.
Bulgaria held the elections while battling a third wave of coronavirus infections that has seen hospital admissions spike.
Voting booths were set up in hospitals and poll workers also took ballot boxes to voters in quarantine.
Support for Borisov's GERB party –– in power almost uninterrupted for close to a decade –– has been eroded by a series of scandals, with protests last year accusing the government of protecting oligarchs.
If borne out, the exit poll results would represent a fall of around nine points from GERB's 2017 performance.
"I have always taken into account what the people decide... let the elections be honest," Borisov said after casting his vote in the absence of journalists.
"The immense support we received from our counterparts in Europe shows the importance of a stable European government in Bulgaria," he said in a statement on Facebook.
Hopes for change
President Rumen Radev, who supported last year's anti-government protests and has been a vehement critic of Borisov, said he had "voted against the destruction of the rule of law".
"These elections are a step towards returning to normality," he added.
Stela Georgieva, 78, was one of those taking advantage of mobile ballot boxes and told AFP: "I hope younger people enter government to bring about change".
Final turnout figures will be keenly watched for any indication that coronavirus infection fears could have kept some voters away, especially among the opposition Socialists' older electorate.
However, overall turnout seems not to have dropped as much as had been feared.
Boriana Dimitrova, head of Alpha Research institute, said: "The election has been marked by the mobilisation of younger, urban voters."
Exit polls suggest that a new populist group, There is Such a Nation, led by sharp-tongued talk show host and Borisov critic Slavi Trifonov, has won around 17 percent, neck-and-neck with the traditional main opposition Socialist party.
The Turkish minority Movement for Rights and Freedoms party, a traditional kingmaker, is behind them on around 11 percent.
Two formations that specifically targeting the votes of those who joined last year's demonstrations look to have garnered around 15 percent of the vote between them.
They are the right-wing Democratic Bulgaria coalition –– whose leader Hristo Ivanov encouraged the protests –– and the Stand up! Mafia out! left-wing coalition, close to Radev.
Ivanov said Sunday he was hoping for a "parliament with more legitimacy to launch a debate on change".
Liliya Bozhilova, 47, came to a Sofia polling station to vote for Democratic Bulgaria with her young son.
"I hope to see the start of a change from this long period during which Bulgaria was in fact governed by one single party. I think that we need new people and new faces," she said.
Bringing up the rear is GERB's current government coalition partner, the nationalist VMRO party, who look like they will manage to clear the hurdle of four percent to gain seats in parliament after leading an aggressive campaign of anti-Roma, anti-LGBT and anti-North Macedonia rhetoric.
Voting stations closed at 8 pm (1700 GMT).
First partial official results, usually expected late Sunday night, might be delayed due to the introduction of machine voting along with the usual ballot paper voting in the majority of big polling stations.
The central electoral committee is due to release the official results by Thursday.