Voters in Lower Saxony are heading to the polls. The elections will decide whether State Premier David McAllister (above right) of the conservative Christian Democrats (CDU) can retain his black-yellow coalition with the open market Free Democrats (FDP), or if his center-left Social Democrats (SPD) opponent, Stephan Weil (above left), will become head of Germany's fourth-largest state.

Weil is currently mayor of Lower Saxony's capital, Hanover.

The northwestern state's elections are viewed as an important test ahead of the September national elections.

The FDP's popularity has waned of late, and a failure to reach the 5 percent threshold needed to remain in the Lower Saxony parliament - a requirement mirrored on the national level - could spell trouble for Philip Rösler, who heads the party and also serves as Germany's economics minister and vice chancellor.

Should the SPD and partners the Greens achieve a majority coalition, it would give them much-needed momentum in their attempt to unseat the Bundestag's ruling CDU-FDP coalition, headed by Merkel.

The SPD's candidate to run against Merkel in September, former economics minister Peer Steinbrück, has seen his party's once clear popularity advantage decline in Lower Saxony on the back of a series of gaffes leading up to Sunday's vote.

Tight race

Recent opinion polls have the two potential coalitions even with 46 percent support in the state.

There are 659 candidates running for the state's 135 parliament seats. In the last election five years ago, the CDU won 42.5 percent of the vote, following by the SPD with 30.1 percent, the FDP with 8.2 percent and the Greens with 8 percent. The socialist Left Party received 7.1 of the 2008 vote, earning a spot in the Lower Saxony parliament for the first time.

The parties will no doubt be hoping for a higher voter turnout this time around. In 2008, only 57.1 percent of those eligible turned up.

There are some 6.1 million eligible voters in Lower Saxony.

Voting ends at 6 p.m. (1700 GMT), when the broadcasters ARD and ZDF plan to release their exit polls. Official results are expected at about 11 p.m.

dr/mkg (dpa, Reuters, AFP, dapd)