The CDU is faced with a leadership vacuum after Merkel's handpicked successor, Annegret Kramp-Karrenbauer, said she would not stand to succeed Merkel as chancellor in elections set for 2021 and would stand down as party leader once another candidate is chosen.

Kramp-Karrenbauer took over as CDU leader from Merkel in late 2018 as part of the long-serving German chancellor's gradual retirement plan, leaving the future of Germany's strongest political force wide open.

While confirming his intention to run for the CDU leadership, sources close to Merz would not confirm whether he intended to aim for the chancellery.

Merz, whose leadership experts say would pull the CDU further to the right, is scheduled to speak at an economic forum in Berlin later on Thursday.

Merz narrowly lost out on the CDU leadership to Kramp-Karrenbauer, who was toppled by a crisis involving the far right in the state of Thuringia, after her party voted alongside them to elect a state premier.

No other candidates have thrown their hat in the ring for the CDU top job, although Health Minister Jens Spahn and Armin Laschet, chairman of the CDU's powerful branch in the state of North Rhine Westphalia, have been tipped as potential successors.

Markus Soeder, head of the CDU's Bavarian sister party, the Christian Social Union (CSU), is also seen as a possible contender.

Australian Associated Press