Deputy Chancellor Sigmar Gabriel has announced his intention to seek Germany's top job in 2017, ending a debate at his Social Democrats party over whether it should even try to unseat Chancellor Angela Merkel.

"Of course I want to become chancellor, if the SPD decides to pick me for it," said Gabriel, who is leader of his party and also economy minister, in an interview published in weekly magazine Stern on Thursday.

Merkel has not said if she would stand for a fourth term at the next elections.

Even though she is facing a growing backlash at home over her decision to open the doors to refugees fleeing war and persecution, Merkel still enjoys strong support in Germany.

Latest opinion polls show backing for Merkel's conservatives at around 36 percent, still commanding a significant lead over the SPD's 24 to 26 percent.

Nevertheless Gabriel has said he thought Merkel could be beaten in the next elections and that he was open to a party referendum to pick the challenger.

The SPD, which has ruled as junior partner in a coalition with Merkel since 2013, is holding its national party congress in mid-December when it is due to elect its chief who, traditionally, would also lead it in subsequent general elections.

An SPD state leader, Torsten Albig, had stunned German political scene in July when he said he suggested that his party should simply campaign to remain Merkel's junior partner rather than seek to replace her.

Gabriel's firm confirmation would serve to "calm speculation" within his party, business daily Handelsblatt said.

SPD Vice Chairman Ralf Stegner called it a "good sign" that Gabriel was throwing his hat into the ring.

Noting that Merkel's Bavarian sister party, the Christian Social Union (CSU), has openly hit out at the German leader over her stance on refugees, Stegner told DPA news agency that it was a good time for Gabriel and the SPD to show their strength.