SEOUL, June 28 (Reuters) - South Korea's factory output fell in May, missing market expectations, on weaker production of machinery and automobiles, official data showed on Friday.

The industrial output index fell 1.2% over the month on a seasonally adjusted basis, after a 2.4% rise in April and compared with a gain of 0.2% tipped in a Reuters survey of economists.

Production of machinery fell 4.4% and cars dropped 3.1%, while semiconductors rose 1.8%, according to Statistics Korea.

On an annual basis, the index rose 3.5%, slowing from the previous month's 6.2% increase but beating a rise of 3.0% expected by economists. (Reporting by Jihoon Lee; Editing by Christopher Cushing)