Chancellor Angela Merkel's successor as leader of Germany's ruling Christian Democrats (CDU) is under growing pressure after the party was forced into second place by the Greens in a series of opinion polls.
Three polls published in three days showed the Greens pulling ahead of the CDU, making them the country's most popular party for the first time since they were founded.
The latest, a Forsa GmbH poll published yesterday, put the Greens on 27 per cent, three points ahead of the CDU - a historical low for the traditional governing party of Germany.
The Greens have enjoyed a surge in popularity in recent months amid growing concern about climate change, biodiversity and plastic waste, and overtook the Social Democrats, their left-wing rivals, earlier this year.
Critics within the CDU have blamed Annegret Kramp-Karrenbauer, who took over from Merkel as party leader in December, for a string of tactical errors.