Polls suggest Merkel's Christian Democrats  will win 22 per cent and come in a distant second to the SPD [Reuters]

Angela Merkel, the German chancellor, is bracing for a sixth straight defeat in state elections amid fears the result in the city-state of Berlin will be a major setback for her governing coalition.

Voters started casting their ballots in Berlin at 8am (0600 GMT) on Sunday in an election widely expected to re-elect Klaus Wowereit, the capital's openly gay mayor for the Social Democrats (SPD).

While Merkel's Christian Democrats (CDU) look set to place second or third in left-leaning Berlin, her junior coalition partners, the Free Democrats (FDP), may crash out of the state legislature for the fifth time in a poll this year.

Opinion polls suggest the CDU will win about 22 per cent of the vote and come in a distant second to the centre-left SPD, who are forecast to win about 31 per cent and stay in power with a coalition with either the Greens or the Left party.

"We are expecting embarrassing results for the CDU," said Al Jazeera correspondent Nick Spicer, reporting from Berlin.

Spicer said the election's main issues have been Berlin's unemployment, which at 13 per cent is double the national average, and rising rent prices.

Pirates emerge

The vote could bring further bad news for Merkel's centre-right coalition if the FDP fail to win at least five per cent of the vote and are ejected from the state assembly.

It would be the fifth time in seven elections this year the FDP failed to win five percent.

Defeat could raise pressure on the party, which has plunged from a record 14.6 per cent in the 2009 federal election, to remove Guido Westerwelle, the unpopular foreign minister. Polls show the FDP at about 2 per cent.
   
Another surprise on Sunday could be the Pirate Party, a German branch of the party that emerged in Sweden five years ago to campaign for reform of copyright and better privacy in the internet age. Polls show the Pirates winning 9 per cent.

Debt debate
   
Merkel, who has been criticised for her leadership during the euro zone crisis, is halfway through a four-year term.

But defeats for her CDU have battered her popularity ahead of a critical vote on euro zone measures in parliament at the end of September.
   
The SPD, in opposition at the national level since 2009, want their likely re-election in Berlin to build up momentum to oust Merkel in the next federal election in 2013.
   
The SPD has ousted or helped defeat the CDU in Hamburg and Baden-Wuerttemberg this year and remained in power elsewhere.
   
The CDU has lost five of six regional votes. A bad result in Berlin, Germany's largest city with 3.4 million, would add to Merkel's woes ahead of a vote in the Bundestag on September 29 to give the European Financial Stability Fund more powers.
   
The euro crisis has crept into the campaign in Berlin, with Merkel using a local radio interview ostensibly on city issues to quash talk of an imminent Greek default .