The young population has fallen from 14.4 million in 1980 to just 8.5 million this year. It is expected to dwindle even further to 6.4 million in 2040 and 4.8 million in 2060, according to Statistics Korea. That means the proportion of people under 24 in the total population has dropped from a buoyant 39.1 percent in 1970 to less than one-sixth or 16.4 percent.

Korea's young population between the ages of nine and 24 has almost halved since 1980, auguring serious trouble ahead.

According to the Education Ministry, 113 elementary schools, 10 middle schools and seven high schools across the country welcomed no new students this year. One percent out of 2,360 high schools, 11.6 percent out of 3,237 junior high schools and 13.8 percent out of 6,177 elementary schools in the country welcomed fewer than 10 new students.

The decline became serious around 2001, when Korea hit the ultra-low birthrate of less than 1.3 children per woman. Analysis of data from 17 metropolitan and provincial governments shows that the number of first graders in high school stood at 524,500 this year, 57,000 fewer than sophomores.

The biggest decline was in the major cities, with the number of high-school freshmen in Gyeonggi Province down 14,100, in Seoul down 11,100, in Busan down 3,628, and in Daegu down 3,198. Next year, their number is expected to drop by 63,000, with Seoul and Gyeonggi Province expected to a decline of 12,000 each, which means teachers have to be let go and schools will close.

The decline will also have an impact on the number of conscripted soldiers Korea depends upon for its defense.

In 2020, the number of high school graduates will stand at 520,000, a similar level to the 510,000 students enrolled in universities and vocational colleges. By 2024, the number of high school graduates will plummet to 420,000. Therefore the number of 20-year-old men who are then available to start their mandatory military service will fall from 350,000 at present to 250,000.