The ruling Czech ruling coalition led by left-wing Social Democrats topped the polls in the first round of elections for Parliament's upper house.

With all the votes counted, no candidate in the race for 27 seats in the 81-seat Senate reached the 50-percent threshold to win outright, the Statistics Office said on Sunday. The top two finishers in each district face next weekend's runoff.

The Social Democrats were first or second in 19 districts contested Friday and Saturday.

The other two coalition members, the centrist ANO movement and Christian Democrats, advanced to the runoffs in nine and eight districts, respectively, giving the coalition a good chance to retain a majority.

The conservative Civic Democratic Party was the best opposition force with seven candidates advancing to the runoffs.

Parliament's lower house dominates the legislative process, but the Senate plays an important role in passing constitutional amendments and approving Constitutional Court judges.

In separate local elections, independent candidates and groupings won the most seats nationwide, some 63 percent.

Led by the new star of Czech politics, billionaire Andrej Babis, the ANO party won in half the 26 major cities, including the capital Prague, cementing its status of a new major political force.

Campaigning on an anti-corruption ticket, ANO's prominent candidate — former head of the Czech branch of corruption watchdog Transparency International Adriana Krnacova — now has a chance to become Prague's mayor.