Voters in Germany's most populous state, North Rhine-Westphalia (NRW), have started going to the polls in elections for the regional parliament.

The current ruling coalition of center-left Social Democrats (SPD), under incumbent state premier Hannelore Kraft, and pro-environment Greens came out ahead in earlier opinion polls, which put them winning a majority by a narrow margin.

Sunday's snap elections were called after NRW's minority government fell when the regional parliament failed to pass a draft budget after just 22 months in power.

Surveys showed Chancellor Angela Merkel's conservative Christian Democratic Union (CDU) trailing the SPD in the state by several points. The CDU's candidate for state premier, Norbert Röttgen, is Merkel's federal environment minister, but he markedly trails Kraft in popularity ratings.

A survey by state broadcaster ARD published on May 3 put the SPD in the outright lead with 38.5 percent of the vote, while predicting the Greens could court a further 11 percent. That puts the pair almost exactly at the 50 percent threshold needed to form a majority.

Merkel's CDU polled at 30 percent in the same survey. Their current coalition allies in the federal government, the pro-business Free Democrats (FDP), came in with a meager 6 percent.

The Left polled at 4 percent, just below the 5 percent required to qualify for seats in parliament, while the relative newcomer Pirate Party enjoyed an estimated 7.5 percent of voter support. That represented a slight drop for the Pirates compared to a previous ARD-commissioned poll.

After five years in power, Merkel's coalition lost the state of North Rhine-Westphalia in 2010. The change cost the national government its majority in the upper house of parliament, the Bundesrat, which represents Germany's 16 states.

The NRW election is one of three state-level ballots in Germany this year. Earlier this month, the CDU-FDP coalition lost power in the northern state of Schleswig-Holstein.

The latest national polls still show the CDU as Germany's biggest party, but suggest that Merkel's center-right coalition would not win a parliamentary majority if elections were held now.

Around 13.2 million people are eligible to vote in the NRW election. Polling stations close at 1600 GMT and results are expected later on Sunday.

tj/srs (AP, AFP)