Budapest's liberal mayor Gergely Karacsony has quit the race to be the opposition's candidate against Hungary prime minister Viktor Orban in next year's general election.

       Earlier this year Hungary's opposition parties announced they were uniting in a bid to oust Orban, who has been PM since 2010.

       Karacsony came in second in the opposition primary last month behind Klara Dobrev, the leftist Democratic Coalition's candidate.

       On Monday, Karacsony said he was joining forces with Peter Marki-Zay -- who came third -- in the second round of the primary.

       Then, on Friday, Karacsony announced he was quitting.

       "After some deliberation, I end the candidate campaign with a clear heart, I ask the organisations supporting me to vote for Péter Márkyi Zay," he said.