Only a few weeks ago, Angela Merkel's conservative opposition Christian Democrats (CDU) and their allies seemed assured of an easy victory. But the latest polls show the Left party winning up to 60 Bundestag seats, which would make it Germany's third-largest political force.

And it could deny an outright majority to Ms Merkel while further weakening Chancellor Gerhard Schröder's ruling Social Democrats (SPD).

Mr Scholz accepted his party was unlikely to win. But he pledged there would be no backroom deals to keep the SPD and Greens in power.