German Chancellor Angela Merkel has announced she will give up leadership of her center-right Christian Democrat Union (CDU) party after 18 years in the post, German media has reported.
This would be in contrast to Mrs Merkel's previous position, in which she has linked the party leadership role to the chancellorship - meaning that she would only remain chancellor if she was party leader.
SPD leader Andrea Nahles, whose party saw support fall to its lowest since 1946, has threatened to end the alliance with Ms Merkel's conservatives if there is no improvement on policy.
Ms Merkel has led the Christian Democrats since 2000 and been chancellor since 2005.
The Greens, who have governed Hesse in coalition with the CDU over the last 5 years, were neck-and-neck with the SPD, also securing 19.8% of the vote.
Hesse's conservative governor, Volker Bouffier, told supporters that "the message this evening to the parties in the government in Berlin is clear: people want less argument, more objectivity, more solutions".
Merkel, 64, had previously indicated that she planned to seek another two-year term as leader of her Christian Democratic Union at a December party congress, but appeared to be moving quickly to acknowledge pressure for renewal as her fourth-term government struggles to gain traction.
This also marked the worst result for the party since 1962. When Hesse last elected its state legislature in 2013 - on the same day that Merkel was triumphantly elected to a third term as chancellor - they won 38.3 and 30.7 per cent, respectively.
Others include two state premiers Armin Laschet and Daniel Guenther, who carry weight after recently leading the CDU to victory in regional elections.
Nahles said on Sunday she would propose a roadmap to allow the SPD to measure the progress of the ruling coalition, which has been plagued by infighting, at a mid-term review next year. Meanwhile, the anti-establishment Alternative for Germany party, which advocates a stricter migration policy, has entered Hesse's Landtag for the first time with 13.1% of the vote and now holds seats in all of Germany's regional parliaments.
Her centre-right CDU party and the centre-left SPD were 10% down on the previous election in Hesse state.
Mrs Merkel's party managed an unimpressive win, narrowly salvaging a majority for its regional governing coalition with the Greens.
Nahles declined to comment Monday on the reports that Merkel might step down as CDU leader. Although the CDU has remained relatively united behind its leader in public, discontent has been building as the party's fortunes have sunk.
Increasing numbers of SPD members are calling for the party to quit government immediately and lick its wounds in opposition, as it is presently polling below AfD nationwide, at 15 percent to the far-right's 16 percent.
And Mr. Bouffier, noting that his party fared better in the Hesse vote than it now does in polls nationally, seems keen to stay in power.
The CDU's general secretary, Annegret Kramp-Karrenbauer, said the coalition needs to identify "three concrete projects for the coming months that we implement".