Poland is holding parliamentary elections, with the conservatives hoping to return to power after eight years in opposition.
Opinion polls in run-up to the election put the Law and Justice party, led by Jaroslaw Kaczynski well ahead of PM Ewa Kopacz's Civic Platform party.
Law and Justice regained the presidency in May when Andrzej Duda won the poll.
About 39% of those eligible had voted by late afternoon on Sunday, slightly higher than the poll four years ago.
Law and Justice is most strongly supported in rural areas and by those close to the country's powerful Roman Catholic Church.
Civic Platform has been damaged after wiretap recordings of senior government figures making controversial remarks were released.
And on Friday, Deputy Justice Minister Monika Zbrojewska was fired after being charged with drink-driving.
'Diseases and parasites'
Europe's refugee crisis also proved to be a key topic of debate before the election. While the government has agreed to take in 7,000 migrants, opposition parties have spoken out against the move.
Last week, Mr Kaczynski was criticised for suggesting migrants could bring diseases and parasites to Poland.
The 66-year-old is not running as prime minister, and has instead nominated Beata Szydlo, a relative unknown, as the party's choice for the post.
However, some observers think Mr Kaczynski will take on the top job himself, if Law and Justice scores a convincing victory.
The result of the election is likely to be closely followed among Eurosceptic nations such as the UK.
While Civic Platform sought close ties with the EU, one Law and Justice party member told Reuters they were keen for "a less bureaucratic, more cost-effective EU that does not seek deeper political integration".