Seoul's population, which currently ranks 29th in the world, will drop by 14 notches by 2030, according to the United Nations' Department of Economics and Social Affairs.
The UN body predicts that Seoul's population, which is 9.77 million this year, will edge up to 9.96 million by 2030. Despite the increase in population, Seoul is projected to drop to 43rd place in 2030. The drop in ranking would be the biggest among the top 30 cities on the list.
Tokyo remains the world's most populous city with nearly 38 million people, followed by Delhi with 25 million, and Shanghai with 23 million. The three cities will remain the world's largest cities in 2030, according to the agency.
While retaining the title of world's most populous city, Tokyo's population is projected to decline to 37 million in 2030.
According to the CIA's World Factbook, last updated in June, South Korea's birthrate is the lowest among OECD countries.