The centre-right GERB party of Bulgarian Prime Minister Boyko Borisov has come first in parliamentary elections with around 25% of the vote, according to partial exit polls published on Sunday evening after polls closed.
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 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.
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.
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%, 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%.
Two formations that specifically targeting the votes of those who joined last year's demonstrations look to have garnered around 15% 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".
Up to six other parties are expected to win seats in parliament, said political analyst Antony Todorov, making it difficult to form the next cabinet.
"It's the absence of an alternative due to the fragmented and unconvincing opposition that explains GERB's hegemony," he added.
The number of voters was being keenly watched and will likely define the strength in the legislature of the new faces who have emerged from the protests.
First partial official results 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.
