Winfried Kretschmann has spent the last five years carefully crafting the image of a pragmatic business-friendly leader of the conservative south-western German state of Baden-Wuerttemberg.

On Sunday it paid off for the 67-year-old former biology teacher when his Green Party emerged for the first time as the biggest party in one of the nation's parliaments after a 6.3-per-cent swing to the Greens in Baden-Wuerttemberg's state elections.

Home to some of Germany's biggest brand names such as Mercedes Benz, Porsche and Hugo Boss, Baden-Wuerttemberg was one of three of Germany's 16 states that went to the polls on Sunday, with elections also held in neighbouring Rhineland-Palatinate and Saxony-Anhalt in the east.

But with five parties – including the anti-immigrant Alternative for Germany (AfD) - set to enter each of the state parliaments, the polls could mark the end of the country's post-World War II tradition of two-party coalitions.

The outcome of the polls raises the prospect of multi-party coalitions in the regional parliaments.

In particular, the Baden-Wuerttemberg result could open the way for the Greens to become an option as a coalition partner to Chancellor Angela Merkel's conservative Christian Democrats (CDU) for next year's national election.

"On the party level I think this is an important testing ground," said Daniela Schwarzer, who heads the Berlin office of the German Marshall Fund of the United States.

A practicing Catholic, Kretschmann has cast himself as father of the state and has ruled out moving to the national political stage.

Kretschmann is already the first-ever Green Party head of government after forging in 2011 a coalition with the left-leaning Social Democrats (SPD), consequently ousting the CDU from power after 58 years at the helm of the state.

Now, Kretschmann's Greens have tightened their grip on Baden-Wuerttemberg by securing 30.5 per cent of the vote – far ahead of the 27 per cent for the CDU, which suffered a humiliating 12-per-cent swing against the party.

"Baden-Wuerttemberg has again made history," said Kretschmann.

With his trademark grey brush haircut, Kretschmann's political ascendency has coincided with the decline of the SPD, which is currently a junior member of Merkel's ruling national coalition.

The SPD vote slumped 10.4 per cent to 12.7 per cent coming in behind the bigger-than-forecast 14.9 per cent garnered by the AfD, which turned the populist rightwing party into the state's third-biggest political force.

However, Sunday's result will make Kretschmann's task of forging a new coalition in the state very complicated.

He has not ruled out teaming up with the CDU or the formation of a multi-party coalition, also incorporating the pro-business Free Democrats.

But his success in Germany's third-largest state could help Merkel forge a new political centre in Germany as the refugee crisis drives right-wing voters away from the CDU and into the arms of the AfD, which surged into the parliaments in each of the states voting on Sunday.

"There is a new phenomenon in Germany is protest voters, who voice their discontent with the established parties," said Schwarzer.

"It is a phenomenon which has already emerged in other countries," she said. "Voting is a valve for them to release their discontent."

Merkel carried out intensive coalition talks with the Greens after the last national election in 2013.

A short time later, the Greens decided to team up with the CDU in Hesse under a close ally of Merkel, Volker Bouffier, which acts as a model for the Greens to enter a conservative-led coalition after the 2017 election.

The Baden-Wuerttemberg premier has also praised Merkel's crisis management and her handling of the refugee crisis.

Polls show that more than 60 per cent of Green Party voters also back Merkel's liberal stance on the migrant issue.

The anti-nuclear Greens rode to power five years ago on the back of the apocalytic images that emerged from Japan in the wake of the Fukushima nuclear disaster and deep opposition to the former CDU-led government's plans for building a new central railway in the state capital Stuttgart.

The chancellor has since moved closer to mainstream Green positions.

In addition to spearheading global efforts to address climate change, Merkel went on to mount a major political U-turn after Fukushima, abandoning her support for nuclear energy and co-opt the Greens platform on ending atomic energy.

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