Germany's social democratic SPD party leader Martin Schulz | John Macdougall/AFP via Getty Images Martin Schulz’s Social Democrats take lead in German election poll Opinion poll puts SPD just ahead of Merkel’s conservatives.

Germany's center-left Social Democrats (SPD) party has overtaken Chancellor Angela Merkel's conservative Christian Democrat Union (CDU) in an INSA opinion poll published in Bild Tuesday.

The SPD gained 1 percent support since last week to climb to 32 percent, just ahead of the CDU on 31. The far-right Alternative for Germany (AfD) would be the third biggest party if elections were held now, polling steady at 11.5 percent. The far-left Die Linke would gain 8.5 percent of the votes and the Greens and the center-right Free Democrats 6.5 percent each.

The SPD's popularity has been rising since Martin Schulz, former president of the European Parliament, was named its candidate to take on Merkel in the bid to become the country's chancellor in the September election.

Schulz on Sunday was formally made party chief and named the SPD candidate in the coming election, winning 100 percent of the vote.