SEOUL, June 30 (Reuters) - South Korea’s factory output in May unexpectedly declined from April but logged the fastest expansion in near 11 years on a year-on-year basis compared to 2020’s pandemic-impacted figures, government data showed on Wednesday. Industrial production last month fell by a seasonally adjusted 0.7%, missing a 0.8% gain forecast in a Reuters survey and following a 1.6% contraction in April, when it logged the biggest contraction since may 2020. However, on a yearly basis, factory output surged 15.6%, the fastest growth since June 2010 as production was seen sharply picking up from sluggish 2020 when the coronavirus pandemic paralysed economic activities and supply chains. (Reporting by Joori Roh; Editing by Christopher Cushing) Our Standards: The Thomson Reuters Trust Principles.