The population of Seoul is forecast to fall from the present 10 million to less than nine million by 2045.
Statistics Korea on Thursday said the number of citizens in the capital will fall from 9.94 million in 2015 to 8.81 million in 2045.
At present they make up a whopping 19.5 percent of Korea’s total population.
The figure has been declining since 2010 as people move to surrounding satellite cities due to rising housing costs and traffic congestion and as state-run corporations and ministries relocated to Sejong City and other parts of the country.
That means that the population of Gyeonggi Province surrounding the capital, which absorbs a large portion of the exodus, is expected to rise from 12.42 million in 2015 to 13.56 million in 2045.
The population of other big cities like Busan, Daegu and eight others are also expected to shrink.
But seven areas including the new administrative capital of Sejong, as well as South Chungcheong Province and Jeju Island are expected to see their populations rise.
As the birthrate keeps declining and the population ages, the economically active population between the ages of 15 to 64 is expected to fall from 37.44 million or 73.4 percent of the population to 27.72 million or 54.3 percent.
Busan (down 38.2 percent), Daegu (down 37 percent) and North Gyeongsang Province (down 33.6 percent) are expected to see the biggest declines in the working population.
In some regions older people will account for the bulk of the populations. South Jeolla Province, North Gyeongsang Province and Gangwon Province are dominated by people in their 40s, who will be in their 60s by 2045.
In South Jeolla Province, the median age is expected to rise to 62.2 and in North Gyeongsang and Gangwon Provinces to 60.9.
The proportion of the population over 65 is expected to surpass 30 percent across the country by 2045, with the exception of Sejong. That means one in three people in Korea will be a senior citizen.