The Czech Republic's Christian Democrats, the junior coalition partner, gained the most seats in Senate elections on Saturday, in a possible setback for Prime Minister Bohuslav Sobotka's Social Democratic party a year before a nationwide poll.

The centre-left ruling coalition, which includes the ANO movement that performed well in regional elections the previous weekend, maintained its majority in the upper house Senate in votes to contest a third of its seats.

Parliament's lower house is the country's main legislative body, and elections for its 200 seats are due in October 2017.

The results of the last two weekends' votes are unlikely to shake the government, although Sobotka's party has lost ground, which he has said was a message for it to find new program ideas.

The coalition is entering its final year with an economy firmly growing, unemployment at the lowest level in the European Union, and a budget set to be balanced for the first time in two decades.

In the regional elections last weekend, the Social Democrats lost to main rival ANO, a centrist group founded five years ago by billionaire businessman Andrej Babis, who is now finance minister and seen as a contender to be the next government's leader.

ANO holds a 5.5 percentage point lead over the Social Democrats in the CVVM institute's latest opinion poll in September with 28.5 percent support.

The Christian Democrats are polling at 6.5 percent but made gains on Saturday, winning nine of the 27 Senate seats contested and becoming the second-strongest party in the chamber, whose support is needed to pass constitutional amendments or sign off on international treaties.

ANO won three seats and the Social Democrats took two.

Turnout in the second round of voting reached 15.38 percent and is traditionally low for mid-term elections. In the 2013 lower house elections the turnout was 59 percent.

Babis's party stormed to a surprise second in the last national vote and was contesting its first regional elections this year. His party's drive against corruption and his business-like approach to government has won votes.

However, as the owner of a conglomerate of over 250 companies from farming to the chemical industry and the media, Babis has faced criticism from across the political spectrum for potential conflicts of interest.