This article is more than 3 years old

This article is more than 3 years old

Angela Merkel’s conservatives have won a state election in their centre-left rival’s heartland, in a stinging blow to the challenger in September’s national vote.

The western state of North Rhine-Westphalia is Germany’s most populous and has been led by the Social Democrats (SPD) for all but five years since 1966.

It is also the home state of Martin Schulz, the Social Democrat seeking to deny Merkel, the German chancellor, a fourth term in the election on 24 September. Schulz had been hoping for a boost after two previous state election defeats sapped his party’s momentum.

Instead, Merkel’s Christian Democratic Union (CDU) won 33% of the vote in the election for the state legislature, with the Social Democrats on 31.2%.

SPD governor Hannelore Kraft’s coalition lost its majority as her junior partners, the Greens, won only 6.4%. The conservative challenger Armin Laschet, a deputy leader of Merkel’s party, was poised to replace Kraft.

“The CDU has won the heartland of the Social Democrats,” said the conservatives’ general secretary, Peter Tauber.

Schulz, who was not on the ballot, told supporters in Berlin: “This is a difficult day for the Social Democrats; a difficult day for me personally as well. I come from the state in which we took a really stinging defeat today.”

He urged the party to focus on the national election. “We will sharpen our profile further – we have to as well,” he said. “We will continue fighting; the result will come on 24 September.”

The SPDs’ national ratings soared after Schulz, a former European parliament president, was nominated in January as Merkel’s challenger. But defeats in two other state elections since late March punctured the party’s euphoria over Schulz’s nomination.

The SPD result in Sunday’s election, the last before the national vote, was the party’s worst in North Rhine-Westphalia since the second world war. In the state’s previous election, in 2012, the SPD beat the CDU by 39.1% to 26.3%.

The pro-business Free Democrats won a strong 12.6% of the vote on Sunday after a campaign headed by their national leader, Christian Lindner. That gave the party, with which Merkel governed Germany from 2009-13, a solid base for its drive to return to the national parliament in September after it was ejected four years ago.

The nationalist Alternative for Germany won 7.4 %, giving it seats in its 13th state legislature. The opposition Left party fell just short of the 5% needed to win seats.

Facebook Twitter Pinterest Martin Schulz on Sunday. Photograph: Felipe Trueba/EPA

The result has given the CDU and Free Democrats a very slim majority. If they cannot agree on a governing alliance, Laschet could opt for a “grand coalition” of the biggest parties with the Social Democrats.

A grand coalition would mirror Merkel’s national government, in which the Social Democrats is the junior partner.

After a blaze of publicity this year, Schulz, who chose not to join the government when he returned to Germany in January, has struggled to maintain a high profile. He has focused on addressing perceived economic injustices, but critics have accused him of providing too little detail on his aims.

Kraft told ARD television she had “asked Martin Schulz to let national politics wait until the election was over”. Asked whether that was wise, she replied: “I said I would take responsibility for that, and I’m doing that this evening.” She resigned as her party’s regional leader.

Merkel’s conservatives sought to portray Kraft’s government as slack on security, and also assailed what it said was regional authorities’ poor handling of education and infrastructure projects. The region of 17.9 million – nearly a quarter of Germany’s population – includes Cologne, Düsseldorf and the Ruhr industrial area.

Merkel’s party seemed keen not to appear too euphoric, insisting that regional issues played a key role. Asked about Germany’s government after September, the chancellor’s chief of staff, Peter Altmaier, said “We always have to keep a cool head … we should not talk about coalitions before the harvest is in.”

National polls show the SPD trailing Merkel’s conservatives by up to 10 points after drawing level earlier this year.