SEOUL (Reuters) - South Korea’s factory output in April unexpectedly declined from March but logged the fastest expansion in almost three years on a year-on-year basis compared to 2020’s pandemic-impacted figures, government data showed on Monday. From March, industrial production fell by a seasonally adjusted 1.6%, the biggest contraction since May last year and missing a gain of 1.5% forecast in a Reuters survey. However, on a yearly basis, factory output surged 12.4%, the fastest growth since October 2018 as production was sluggish in the second quarter of last year because of the outbreak of the coronavirus pandemic. Reporting by Jihoon Lee, Cynthia Kim; Editing by Christian Schmollinger Our Standards: The Thomson Reuters Trust Principles.