The outgoing centre-right coalition of Prime Minister Ingrida Simonyte has seen its popularity eroded by high inflation that topped 20 per cent two years ago, by deteriorating public services and a widening gap between rich and poor.
"I got bored with the old government," Hendrikas Varkalis, 75, said after casting his vote in Panevezys, about 100km northwest of the capital Vilnius.
"I want something new."
The polls are tipping Lithuania's Prime Minister Ingrida Simonyte will lose the election. (AP PHOTO)
Polling stations opened at 7am (3pm AEDT) on Sunday and close at 8pm (4am Monday AEDT), with results expected after midnight local time.
Opinion polls suggest Simonyte's Homeland Union will win just nine per cent, behind the Social Democrats on 18 per cent and the anti-establishment Nemunas Dawn on 12 per cent, although the eventual shape of a future coalition will depend on how smaller parties perform.
The Baltic state of 2.9 million people has a hybrid voting system in which half of the parliament is elected by popular vote, with a five per cent threshold needed to win seats.
The other half is chosen on a district basis, a process that favours the larger parties.
If no candidate gets more than 50 per cent of the vote in a district, its top two candidates face each other in a run-off on October 27.
Domestic issues have loomed large in the election campaign, with the Social Democrats vowing to tackle increased inequality by raising taxes on wealthier Lithuanians to help fund more spending on health care and social spending.
But national security is also a major concern in Lithuania, which is part of the eastern flank of NATO and the European Union and shares a border with the Russian exclave of Kaliningrad as well as with Belarus, a close Moscow ally.
Three-quarters of Lithuanians believe that Russia could attack their country soon, a Baltijos Tyrimai/ELTA poll found in May.
The main parties strongly support Ukraine in its war with invading Russian forces and back increased defence spending.
