SEOUL (Reuters) - A South Korean presidential candidate dropped out on Thursday, throwing his support to conservative Yoon Suk-yeol in a surprise move that could tip the balance of next week's closely fought election toward the conservatives.

       Yoon, flag bearer of the People Power Party, the main opposition to the governing liberal party, joined with Ahn Cheol-soo of the People Party, who had been running a distant third.

       "We firmly believe that today's announcement would realise a perfect government change," Yoon and Ahn said in a joint statement issued at a news conference announcing the merger.

       The shake-up less than a week before Wednesday's election is bad news for Lee Jae-myung, representing President Moon Jae-in's Democratic Party. Moon is barred by term limits from seeking reelection.

       A survey by Realmeter released on Wednesday, the last day for publication of polls under election rules, showed 46.3% of respondents favoured Yoon, with 43.1% preferring Lee.

       (Reporting by Hyonhee Shin; Editing by William Mallard)