Voting began on Sunday in Germany's most populous state where Angela Merkel's conservatives face a defeat that could give the left momentum before next year’s federal election and fuel criticism of the chancellor's European austerity drive.
North Rhine-Westphalia (NRW), an industrial state in western Germany with an economy and population the size of the Netherlands, has a history of influencing national politics.
First exit polls were due at 1600 GMT and expected to show Hannelore Kraft of the centre-left Social Democrats (SPD) trouncing her Christian Democrat (CDU) rival Norbert Roettgen, who is Merkel's environment minister.
“The SPD will get back in,” said Helmut Krah, a voter in the NRW capital Duesseldorf who was window-shopping with his wife on the elegant Koenigsallee. "I'm voting for them not because they are good but because the others are so bad.” The vote may bolster SPD fortunes and make Merkel look politically vulnerable for the first time.