Angela Merkel said she would step down as Christian Democratic Union party chief but remain chancellor in October.
Angela Merkel's Christian Democrats vote on Friday to decide who replaces her as party leader and moves into pole position to succeed her as German 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 Germany, Europe's biggest economy, should contribute more to the European Union.
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 since her divisive decision in 2015 to keep German borders open to refugees fleeing war in the Middle East.
The new CDU leader will be chosen by 1,001 delegates who vote at a party congress in Hamburg. The winner will likely lead the CDU in the next federal election due by October 2021.
TRT World's Assed Baig has more.
A survey by pollster Infratest dimap for broadcaster ARD on Thursday showed 47 percent of CDU members favoured 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 Wolfgang Schaeuble.
Economy Minister Peter Altmaier, a Merkel ally, said: "I am convinced that with Annegret Kramp-Karrenbauer we have the best chance of the CDU winning an election," adding she would be the most dangerous candidate to face the centre-left Social Democrats and the ecologist Greens.
Kramp-Karrenbauer's trump card is her record as former state premier in Saarland, where she led a broad coalition with the Greens and pro-business Free Democrats, alliance-building skills useful in Germany's fractured political landscape.
Kramp-Karrenbauer, 56, has differentiated herself from Merkel on social and foreign policy by voting in favour of quotas for women on corporate boards, opposed by Merkel, and by taking a tougher line on Russia.
She told Reuters last week Europe and the United States should consider blockading Russian ships over the Ukraine crisis.
But on what lies ahead for the CDU, Kramp-Karrenbauer says: "I have no particular recipe."
By contrast, Merz takes clear positions that appeal to rank-and-file party members hungry for a more clearly defined party after 13 years under Merkel as chancellor. He wants tax cuts, a stronger EU and a more robust approach to challenging the far-right.
Merz will benefit from the fact that 296 of the delegates at the congress - almost a third - will be from his home state, the western region of North Rhine-Westphalia.
One senior CDU official, speaking on condition of anonymity, said many delegates were undecided before the congress and could be swayed by how the candidates present themselves on Friday. "It could come down to the speeches on the day," he said.