The working-age population made up 74.3 percent of the whole in 2015, the highest among OECD nations, but will plummet to be the smallest in 2065 at 47.9 percent.

It expects the population to peak at 52.96 million in 2031 and then gradually decline to 43.02 million in 2065. But the working-age population is expected to dwindle already next year after peaking at 37.63 million this year, plunging by 300,000 every year from 2020 to reach just 20.62 million in 2065.

Korea's population is expected to shrink by 8 million over the next 50 years. The working-age population aged 15 and 64 is expected to dwindle by 300,000 every year, starting from next year, according to projections released by Statics Korea on Thursday.

By 2115, Korea's population will stand at just 25.82 million, the same as North Korea's now. These demographic changes are similar to Japan's, but Korea is worse off in the long run.

Korea's population structure now resembles Japan's 10 to 15 years ago. Japan's population was 127 million last year, with senior citizens accounting for a whopping 26.3 percent. Korea is expected to reach that stage in 2032.

But others say the situation will not a catastrophe because Japan is still the world's third-largest economy despite its prolonged recession. However, demographers say the situations of the two countries are very different.

"It does not make sense to compare Korea with the world's third-largest economy. The size of the domestic market and economic capacity are completely different," said Cho Young-tae, a professor at Seoul National University.

Japan's working-age population between ages 15 and 64 is 77.27 million, more than Korea's entire population.

Cho explained that neighboring countries like China, Korea and Taiwan grew up buying Japanese products when their economies were still immature, whereas Korea is aging along with its markets, so demand for its products is decreasing. Also the future of its export mainstays such as cars and smartphones is uncertain.

The working-age population accounted for 60.8 percent of the entire population in Japan last year compared to Korea's 73.4 percent, but the ratio will be reversed in 2065, when Japan's working-age population will be at 50.8 percent to Korea's 47.9 percent. By that time, elderly people will account for 36.3 percent of the population in Japan but 42.5 percent in Korea.

