The looming decline came as the number of births continued to drop. South Korea's total fertility rate -- the average number of children a woman bears in her lifetime -- stood at 1.17 in 2016, compared with 1.65 in 1993.

A growing number of South Koreans have fewer babies due mainly to economic burden amid a prolonged economic slowdown.

Still, South Korea's aging population could continue to grow due to progress in medical technology.

The number of South Koreans over 65 accounted for 13.2 percent of the country's population in 2016, Statistics Korea said. It said the ratio of people aged over 65 could reach 24.5 percent of the population by 2030 before hitting 41 percent by 2060.

Nations become an "aged society" if people aged over 65 years make up 14 percent and more.

The statistics office said cancer killed 150.8 of every 100,000 South Koreans in 2015, making the disease the No. 1 cause of death.

Heart disease is the second leading cause of death in the country.

Separately, the statistics office said the number of mobile phones came to 60.28 million in 2016, up 4.1 percent. The numbers indicate that some people use several mobile phones. (Yonhap)