Berlin, Germany: Martin Schulz on Sunday officially became Chancellor Angela Merkel's chief challenger in Germany's September general election.

Schulz was unanimously elected leader of the Social Democrats (SPD) at a one-day party congress and will lead the leftwing effort to unseat the conservative Merkel who is seeking a fourth term as German chancellor.

His decision to leave the European Parliament, which he headed for five years, and be a candidate to lead Germany has given the Social Democrats a new lease of life since party leader Sigmar Gabriel asked him to take the reins in January.

Opinion surveys have recorded a 10-point jump for the SPD in recent weeks and some polls put it ahead of the conservative bloc of Merkel, who is trying to win a fourth term.