Germans in the small western state of Saarland vote on Sunday in a regional election that could deliver an upset to Chancellor Angela Merkel and hurt her prospects of winning a fourth term in September's national election.

The election carries significance as it is the first of three regional votes ahead of the Sept. 24 federal vote and as it offers an opportunity for the parties to build - or lose - momentum in their quest to prevail at national level.

The vote is the first electoral test for the Social Democrats under their new leader, Martin Schulz, who has re-energized the centre-left party with a promise to tackle inequality that is resonating with many voters tired of Merkel.

This time every vote really counts, an unusually impassioned Merkel told a rally in Sankt Wendel, near Germany's border with France and Luxembourg, on Thursday.

Take my words seriously, she said in a last-gasp effort to drum up support for her conservative Christian Democrats (CDU).

Like federal Germany, Saarland is currently governed by a ‘grand coalition' of Merkel's conservatives and the Social Democratic Party (SPD). But polls suggest a left-leaning ‘red-red-green' alliance of the SPD, the far-left Linke party and the environmentalist Greens - or even a ‘red-red' coalition if the Greens fail to win enough votes - could emerge after the vote.

A three-way leftist alliance in Saarland would be the third at state level after Berlin and the eastern region of Thuringia could give impetus to a similar format at national level.

One opinion poll released last week showed support for the SPD and the conservatives was even at 32 percent nationally. But the Deutschland trend poll also showed 44 percent of voters wanted the SPD to lead the next government, compared with 33 percent in favor of Merkel's conservatives taking the lead.

Under Merkel, Germany has enjoyed economic growth and high employment, but the gap between rich and poor has grown.

Schulz is trying to win over dissatisfied working class voters with a message of social justice. The SPD, Linke and Greens have discussed refraining from attacking each other during the national campaign. Schulz is wary of talking about coalition formations before the state and federal elections, keen to maximize SPD support.

The same applies in Saarland as at the federal level we want to be the strongest party, he told weekly newspaper Bildam Sonntag. Whoever then wants to govern with us, is very welcome to come to us.