Slovaks have began voting in the first round of a presidential election that Prime Minister Robert Fico is poised to win, sparking concern that his party could monopolise power.

Victory on Saturday for the ex-Communist Fico would mean the presidency, parliament and government is controlled by the same party, the Social Democrats, for the first time since Slovakia won independence in 1993.

Fico, 49, has earned valuable political capital during his two terms as prime minister with an anti-austerity agenda tempered by fiscal discipline, according to the AFP news agency.

He commands around 35 percent support in opinion polls and is most likely to face non-partisan millionaire-turned-philanthropist Andrej Kiska in a possible runoff vote set for March 29.

Kiska, 51 and without a Communist party past, has scored 24 percent support in pre-election polls and is seen as politically untainted.

Other, less popular contenders include actor Milan Knazko, a leading figure from the 1989 Velvet Revolution that peacefully dismantled Communism in what was then Czechoslovakia; Radoslav Prochazka, a constitutional lawyer; and former parliament speaker Pavol Hrusovsky, a Christian Democrat.

Presidential system

Fico would need to get more than 50 percent of votes cast on Saturday to avoid a runoff.

The prospect of Fico consolidating his power has galvanised both the political class and voters in the country of 5.4 million, which joined the European Union in 2004 and the eurozone in 2009.

The election has become "a referendum on Robert Fico's government and the concentration of power", Grigorij Meseznikov from the Bratislava-based Institute for Public Affairs told AFP.

A Fico win would trigger a reshuffle in his one-party government, but it would still control a comfortable 83-seat majority in the 150-member parliament until the 2016 general elections.