An election in Germany's most populous state is serving as a prelude to September's national vote and could give conservative Chancellor Angela Merkel new momentum in her quest for a fourth term or offer her center-left challenger some relief.
Kraft announced that she was stepping down as the Social Democrats' regional leader. Even being forced into power-sharing in its bastion represents a huge setback for the SPD, especially this close to the national vote.
The NRW, which encompasses major cities, including Cologne and Dusseldorf, as well as the Ruhr industrial region, has been mostly ruled by the center-left Social Democrat (SPD) Party for more than half a century.
Instead, Merkel's Christian Democratic Union won 33 percent of the vote in the election for the state legislature, with the Social Democrats trailing on 31.2 percent. The SPD are now junior partners in Germany's governing coalition.
Last weekend, they were beaten by German Chancellor Angela Merkel's party in Schleswig-Holstein in Germany's far north.
Sunday's vote is the last state election before the federal elections set for September 24, and is seen as a vital pre-duel between Chancellor Angela Merkel's Christian Democratic Union (CDU) and Martin Schulz's Social Democratic Party (SPD).
Compared with the election five years ago, Merkel's Christian Democrats managed to gain around 8 percentage points, while the Social Democrats lost around 8.5 percentage points of the vote. But defeats in two other state elections since late March punctured the party's euphoria over Schulz's nomination.More news: Conservative drops out of Iran election to back hard-liner
She also urged voters to look at her government's economic record, noting that with 7.5 per cent unemployment, the state fares worse than the national rate of 5.8 per cent.
The likeliest outcome appears to be a "grand coalition" of the biggest parties led by whoever finishes first.
Around 13m Germans are eligible to cast a vote in the state elections in North Rhine-Westphalia (NRW) today, which is home to nearly a quarter of the country's population.
But she insisted that "the national election campaign is only beginning now". It is Schulz's home territory, though he isn't on the ballot, and home to 17.9 million people, almost a quarter of Germany's population.
They have sought to portray Kraft's state government as slack on security and also criticized its handling of education and infrastructure projects.
In the past several months, some opinion polls have shown that Schulz, a former president of the European Parliament, will have an edge over Merkel in the coming federal elections.