** Shares of Zip Co ZIP.AX rise as much as 20.2% to A$1.430, posting their biggest intraday percentage gain since December 7, 2023

** Stock is the biggest percentage gainer in the benchmark S&P/ASX 200 index .AXJO, which is up 1.1%

** The buy now, pay later firm announces a share buyback plan of up to A$50 million ($30.06 million)

** Stock last up 12.6%, trimming YTD losses to 54.9%

($1 = 1.6633 Australian dollars)

(Reporting by Aaditya Govind Rao in Bengaluru)

((Aaditya.govindrao@thomsonreuters.com))