(Updates with details, economist's comment, survey findings)
SEOUL, Oct 30 (Reuters) - South Korea's industrial production fell the most in six months in September from August as strikes hit top automakers Hyundai Motor Co. and Kia Motors Corp., denting a recent run of upbeat data.
Industrial output fell by a seasonally adjusted 2.1 percent in September from August, data released by Statistics Korea data showed on Wednesday. August's reading was revised down to 1.6 percent growth from a preliminary 1.8 percent rise.
The output numbers showed the sharpest decline since March and were worse than any individual forecast provided in a Reuters survey of 13 economists. The median forecast from the survey was a 0.4 percent fall.
The data came after central bank data showed last week Asia's fourth-largest economy grew a seasonally adjusted 1.1 percent in the third quarter over the previous quarter, beating market expectations and matching a 2-year high set in the April-June period.
Auto production plunged by a seasonally adjusted 18.6 percent in September from August, the biggest monthly loss in nearly five years and it alone pulled down the overall output index by 2.36 percent, the data showed.
"While the data showed a sharp contraction in output, this doesn't signify a major setback for the economy," said Lee Chul-hee, chief economist at Tong Yang Securities, also blaming disruption in operations at the country's top automakers.
Statistics Korea data showed without the disruption of the car industry, overall industrial output would have posted a small gain.
On a brighter note, the data showed that service-sector output rose by a seasonally adjusted 0.3 percent in September on a monthly basis following a revised 0.8 percent rise in August.
A central bank survey, released early in the day, showed the confidence among South Korea's manufacturing firms rose to the highest in 22 months in terms of their assessment of business outlook for the coming month.
Another survey conducted by the Bank of Korea also showed early this week the consumer confidence rose to a 17-month high, with poll respondents saying they were more willing to increase spending.
On an annual basis, industrial output fell 3.6 percent in September after a revised 3.2 percent rise in August, the data showed, compared with a median 1.2 percent rise tipped in the Reuters survey.
South Korea's industrial output closely mirrors its exports, as the country is home to some of the world's biggest manufacturers of cars, ships and smartphones. Exports in September fell by 1.5 percent from a year earlier, weighed in part by fewer working days due to the Chuseok holiday break.
(Reporting by Se Young Lee; Editing by Eric Meijer and Choonsik Yoo)