It was also the highest nonredemption ratio since the 13 percent recorded in 2014.

Last year's increase was attributed to the country's job instability among youths, which made borrowers less willing to pay back debt due to jitters over their future.

"There is a high possibility that the rate increase stemmed from job instability and the recent sluggishness of the local economy," a government official said.

As of end-August in 2017, 2.13 million college graduates held nonregular jobs, or roughly 33 percent of the country's total temporary workers.

South Korea, Asia's fourth-largest economy, remains dogged by high youth unemployment. The jobless rate for people aged 15-29 came to 9.8 percent last year, the highest level since 2000 when the government began compiling related statistics.

The youth unemployment rate has remained high this year, reaching 10 percent in the first quarter and 10.1 percent in the second quarter before falling to 9.4 percent in the third quarter. (Yonhap)