Germany's centre-left Social Democrats (SPD) edged ahead in the race towards September elections on Tuesday, beating Angela Merkel's conservatives in a poll for the first time since 2006.

The survey of 2,504 people for the NTV broadcaster had the centre-left party in the lead on 23 percent, with Merkel's CDU-CSU alliance trailing behind on 22 per cent.

The two parties are currently in a governing coalition led by the conservatives, with Merkel due to step aside after elections on September 26.

The CDU-CSU alliance enjoyed a strong lead in the polls going into the summer, but has been on the back foot amid a series of missteps from Armin Laschet, the conservative candidate to succeed Merkel.

In July, Laschet was pictured laughing in the background with local officials while Germany's president gave a speech mourning the victims of deadly floods.

Since the disaster, the conservatives have been unable to halt a falling trend in popularity.

The Greens, who enjoyed a surge in support earlier in the year, have also failed to regain momentum after their chancellor candidate Annalena Baerbock was embroiled in a plagiarism scandal.

Until a few weeks ago, the SPD had been polling so badly that many had written off the possibility that it would be part of the next government.

But surveys last week already showed the centre-left party neck-and-neck with the conservatives, who have led Germany in four coalitions since 2005 when Merkel took office.

A survey published Friday also showed 41 per cent of voters would prefer the SPD candidate Olaf Scholz to be the next chancellor, compared with just 16 per cent for Laschet.