Poland's conservative Law and Justice (PiS) party has won an outright majority in general election on anti-refugee rhetoric and welfare promises, ending eight years of centrist rule.
Analysts said the next government's first moves would be closely scrutinised, given the risk that nationalist policies could inflame tensions with the European Union and Russia.
An exit poll by public broadcaster TVP showed the PiS, led by eurosceptic Jaroslaw Kaczynski, scored 242 out of 460 seats in the lower house of parliament, ousting the governing Civic Platform (PO) liberals who took 133 seats.
Kaczynski declared victory yesterday and his first step was to pay tribute to his twin bother, the late president Lech Kaczynski, who died in a 2010 plane crash in Smolensk, western Russia.
"Without him, we wouldn't be here today. His spirit is stronger than his body. We must keep his memory alive," Kaczynski said, also recalling 95 others who died in the crash.
"This is the first time in the history of Polish democracy that a single party has scored a(n) (outright) majority" in the Sejm, the lower house of parliament, he said.
Prime Minister Ewa Kopacz conceded the PO's defeat after its two consecutive terms in office.
"The Poland we leave to the election winners" is one of economic and social progress, she told supporters in Warsaw.
Leftist parties were voted out of parliament for the first time since the advent of democracy after communism's demise in 1989.
Turnout was 51.6 per cent, a record high, according to the TVP exit poll.
Kaczynski, 66, did not run for prime minister but is expected to call the shots in the next government. He is seen as a master of political intrigue, pulling the strings behind the scene.
While he has yet to formally name the new premier, he previously anointed Beata Szydlo, 52, as the PiS's choice after she ran a victorious presidential campaign for Andrzej Duda, a newcomer to politics who ousted PO ally Bronislaw Komorowski in May.
"After eight years in opposition, Kaczynski is making a big comeback," Warsaw political analyst Eryk Mistewicz told AFP.
Poland has become an east European heavyweight after a quarter century of explosive growth and vastly-improved living standards since communism fell. But bread-and-butter issues coupled with fears sparked by Europe's migrant crisis dominated the campaign.
