In addition, the elections are two years early due to a collapse of a complicated ruling coalition.

The outgoing government is led by the conservative Law and Justice party (PiS) of prime minister Jaroslaw Kaczynski.

His coalition partners which were ousted from the government in September, the right-wing nationalist League of Polish Families and the populist rural Self-Defence Party, are unlikely to pass the parliamentary threshold in Sunday's poll.

Mr Kaczynski's key rival in Sunday's elections is Donald Tusk, the leader of the pro-business and pro-European Civic Platform (PO), who is promising to improve Poland's problematic relations with other EU countries and bring along stability after months of political turmoil.

Mr Tusk has also said he will cut down red tape for businesses, introduce a 15 percent flat tax and improve the country's absorption of EU funds.

But according to the most recent polls, the PO party would find it difficult to form a ruling coalition, as its pre-election scores with its most likely coalition partner - the Polish Peasants' Party - would still not be enough for the parliament majority capable of breaking the presidential veto.

The president's office is currently held by Lech Kaczynski, twin brother of the conservative prime minister.

Another possibility would be for Mr Tusk's liberal conservatives to join forces with the Left and Democrats (LiD), a newly formed alliance of ex-communists and small centre-right parties led by ex-president Aleksander Kwasniewski.

On the other hand, analysts suggest that if previous election scenarios repeat themselves, the conservative Law and Justice Party could still emerge as a winner despite marginally lagging behind their major competitors hours ahead of the poll.

In that case, insiders predict Mr Kaczynski would probably try to fish in Civic Plaform's waters to get backing from some of its deputies. Mr Kaczynski has previously argued that it would be unacceptable to get together with ex-communists such as Mr Kwasniewski.

"We could see a boost of popularity of Civic Platform shortly ahead of the elections but it is too early to guess who will come out as the winner," Sociology Professor Andrzej Rychard told leading Polish daily Rzeczpospolita on Friday (19 October).

He argues that political sentiments in his country are changing not just day by day but hour by hour.

"It's hard to predict what will happen. There can be even an event which will look like having nothing to do with the elections but will eventually influence them," he added, stressing that some polls suggest over 10 percent of voters still have not decided who they will back on Sunday.