The government chopped its full-year growth forecast to 1.74 percent, down from 2.31 percent predicted in August and 2.4 percent in May, according to the Directorate General of Budget, Accounting and Statistics.
Slowing demand for liquid crystal display panels, falling shipments of petrochemical products and stiff competition from China were to blame for the worse-than-expected performance, the agency said in a statement.
Weak domestic demand also weighed on the economy, it added.
However, growth forecast for the three months to September stood at 1.66 percent, up from a previous estimate of 1.58 percent.
The GDP was forecast to rise 2.59 percent in 2014, down from 3.37 percent outlined previously as the agency expected many of the factors that had been hampering growth to remain next year.