South Korea has shown the most extreme demographic shift in the last four decades with its population aging at the fastest pace among advanced economies, data showed Tuesday.

Koreans aged 65 or older accounted for 12.2 percent of the total population of about 50 million, the 30th-highest proportion among the populations of the 34 members of the Organization for Economic Cooperation and Development, according to an analysis by the Korea Institute for Industrial Economics and Trade.

But in terms of the pace of aging, using 1970 as the base year, South Korea ranked first, with the elderly population growing four times up until 2013, which is more than double the OECD average of 1.6 times, data showed. Japan was No. 2 with 3.6 times, and Finland followed with 2.1 times.

The proportion of children aged 0-14 years came to 14.7 percent, which is nearly half of top-ranked Mexico's corresponding figure of 28.4 percent and below the OECD average of 17.4 percent, the KIET said.

The proportion of the economically productive population aged 15-64 years was 73.1, surpassing the OECD average of 66.6 percent.

"As South Korea's birth rate has fallen at the fastest pace among the OECD countries, the decreasing number of economically productive population and retirement of baby boomers could add uncertainties to the nation's future," the KIET said. (Yonhap)