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German Chancellor Angela Merkel has given an emotional farewell speech to her ruling Christian Democrats (CDU), as she steps down as party leader.

"Our liberal values must be defended, internally and externally," she said.

She hinted that she was backing Annegret Kramp-Karrenbauer to succeed her, praising her electoral performance as chief minister of Saarland.

Ms Kramp-Karrenbauer's chief rival in Friday's CDU vote is millionaire corporate lawyer Friedrich Merz.

The third candidate, health minister Jens Spahn, appears to have less chance of winning.

Ms Merkel's speech was punctuated by applause and she got a standing ovation of more than six minutes at the end. CDU delegates at the congress in Hamburg also held up signs saying "Thanks boss".

Then the conservative party paid tribute to Ms Merkel, with a video showing highlights from her 18-year CDU leadership. The soundtrack was the 1960s hit Days, by The Kinks.

In her speech she warned of tough challenges ahead, including climate change, maintaining European unity and coping with Brexit.

She reminded the CDU of other electoral successes last year, avoiding mention of this year's setbacks in state elections, which were heavy blows for her.

"I don't need to be party chairman to remain bound to this party. And I'm still chancellor," she said.

She stressed that the CDU stood for human dignity, and praised the late US President George Bush Senior and late German Chancellor Helmut Kohl for reuniting Germany in 1990. She was at the funeral of George HW Bush on Tuesday.

Speaking of the end of the Cold War, she told the CDU that "at that decisive time he [Mr Bush] trusted Chancellor Kohl... he understood how politics must serve everyone".

She expressed "overwhelming gratitude" for having had the role of CDU leader. "The future will test our values... we must always approach work joyfully," she said.