Angela Merkel bowed out as leader of her Christian Democrat Union party (CDU) on Friday with an emotional speech to her conservative party as it met to pick her successor, a person who will move into pole position to become Germany's next chancellor.

The frontrunners are Annegret Kramp-Karrenbauer, a Merkel protege seen as the continuity candidate, and Friedrich Merz, a Merkel rival who has questioned the constitutional guarantee of asylum to all "politically persecuted" and believes Europe's biggest economy should contribute more to the European Union (EU).

Merkel said in October she would step down as party chief but remain chancellor, an effort to manage her exit after a series of setbacks that have come since her divisive decision in 2015 to keep German borders open to refugees fleeing war in the Middle East.

Merkel, 64, told the CDU congress in Hamburg of her gratitude for the chance to have served as party chief for 18 years, 13 of which were as chancellor, during which she came to dominate European politics as its key crisis manager and consensus-builder.

"It has been a great pleasure for me, it has been an honor," she said to a standing ovation lasting nearly 10 minutes, and fighting to hold back tears.

Outlining the multiple challenges facing Germany, from rapidly changing technology and climate change to the global shift away from multilateralism and defending national interests, she said: "In times like these, we will defend our liberal views, our way of life, both at home and abroad."

"The CDU in 2018 must not look back but look forward, with new people [...] but with the same values," added Merkel, who has said she would remain neutral on her successor as party chief.

The new CDU leader will be chosen by 1,001 delegates who will vote at the congress later on Friday. The winner will likely lead the CDU in the next federal election, which will take place in October 2021 at the latest.

A survey by pollster Infratest dimap for broadcaster ARD on Thursday showed 47 percent of CDU members favored Kramp-Karrenbauer compared with 37 percent for Merz and 12 percent for Health Minister Jens Spahn.

Merz, 63, who lost out to Merkel in a power struggle in 2002 and is returning to politics after a decade in business, is backed by CDU members tired of Merkel's consensual politics. He won support this week from party veteran and former finance minister Wolfgang Schaeuble.

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