The German ruling party was dealt a blow in a landmark state vote on Sunday ahead of the 2013 national elections, latest result of the exit polls showed.

Merkel's right-wing Christian Democratic Union (CDU) was reported to have garnered around 25.5 percent of the votes in election at North Rhine-Westphalia, at the country's most populous state and home to the Ruhr Industrial Region.

It trailed the major opposition rival Social Democrats (SPD), which claimed some 38 percent of the total votes, shedding around nine points from the previous election in 2010, according to exit polls published by local media.

This has been the third state-level vote this year after Merkel's center-right ruling coalition got setbacks in the northern state of Schleswig-Holstein.

It promised strong momentum to German left wing ahead of the federal election next year, as the state is home to one sixth German voters.

Hannelore Kraft, candidate of the center-left Social Democrats (SPD), is set to beat her Christian Democrat (CDU) rival Norbert Roettgen, the environment minister in Chancellor Merkel's cabinet.

Voters chanted slogans such as "the SPD will get back in" on the street of the North Rhine-Westphalia capital Duesseldorf, saying their votes switching towards the left were not because "they are good but because the others are so bad."

"When you have worked hard, it's a good feeling when the day of the election comes," said Hannelore Kraft, who led the Social Democrats in the state election.

The CDU's defeat signaled that Germany's most populous and most important industrial state have choose to turn down Chancellor's Merkel for her tough fiscal discipline in tackling the euro zone debt crisis.

Polls in the state usually presage the whole country political landscape, as Merkel rose to power following a landslide victory by her CDU party in this west German state in 2005.

The newly rising Pirate Party, which is established on internet freedom and more direct participation in politics, got around 8 percent of the votes and is assured of its fourth regional parliament seat consecutively.

Nevertheless, national polls so far showed that Merkel's conservatives still claim the most seats in German parliament, before the advent of the national election next year, it is widely tipped that Merkel's CDU will still hold on to the power.