The co-leaders of Germany's Greens party, Omid Nouripour and Ricarda Lang, said on Wednesday they would quit after a series of election blows that saw their party ejected from two regional parliaments.

The move comes at a time of deep turbulence for the governing coalition of Social Democrat Chancellor Olaf Scholz, buffeted by voter worries over the scale of the economic challenges facing Germany and by fierce debates over migration.

"The result in Brandenburg on Sunday is a sign our party is in its deepest crisis for a decade," Nouripour told a news conference. "It is time to lay our beloved party's fate in others' hands."

A new leadership will be elected at the party's upcoming congress in mid-November, Nouripour added.

The Greens failed to clear the five per cent hurdle needed to enter parliament in Brandenburg on Sunday and in Thuringia earlier in September. Along with their SPD and Free Democrat coalition partners, they also suffered big losses in their vote share in elections in Saxony and for the European Parliament this year.

The party needs to prepare for a dramatically changed political climate, Lang told the same news conference.

A new left-wing populist party and the far-right Alternative for Germany (AfD) have outperformed all three coalition parties this year, while the main opposition conservatives are leading in national polls.

"Next year's election is not just any election," Lang said, referring to a scheduled national vote. "(It will be a choice between) a country focused on achieving prosperity by sticking to climate neutrality or a country run by people who want to back away from all that."

The position of Robert Habeck, a senior Greens party member who is Scholz's deputy and Germany's economy minister, is not directly affected by the co-leaders' decision.

The parliamentary leader of Scholz's centre-left SPD, Katja Mast, said she believed the Greens would want to stay in the governing coalition.

"I assume this is a reorganization within the Green Party and not within the government and the Greens benches in parliament," she said.

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